And we all roll merrily on...

Leaving the ice wasn't and isn't the end of the ANDRILL project, or the SMS scientific effort.  It is only the beginning of years of work based on this core and the other information collected in our intense 2-3 months on the ice.  

Much of the team is meeting again this week here in Tallahassee, Florida at the university to review what progress each of the discipline teams have made in analyzing their samples, visit the core again (like a long lost friend), select additional samples to be taken from the other side of the working 1/2 of the core, the one we didn't touch while on-ice, and to make plans for future collaborations, meetings, and drill hole proposals. The heat,

 humidity, trees and insects make it a very different environment

 than where we saw each other last.

The primary reason we are meeting here is that Florida State University houses the Antarctic Core Library.  Every sediment core that has been drilled in Antarctica (remember there aren't that many) is stored here in a climate controlled room.  We suited up in heavy coats and suits to go in to take a look.  

Looking at innocuous rows of shelves and boxes, it felt a little like I was peering into the government warehouse at the end of the first Indiana Jones movie - who knows what is in each box!?  Only I do know.  I know what the depth numbers mean, I recognize the acronyms of the projects and know where each one was taken from.  I know exactly how much trouble, sweat, teamwork, and expertise each box represents.  And I know what kind of 

information we can learn from them.  

Thanks ANDRILL!  Your big picture vision of a multi-national, interdisciplinary team has made an incredible difference to me, the other ARISE educators, and everyone we have had a chance to share the experience with!

Slice it Thin

The purpose of making thin sections is to create a thin, polished slice of rock 30 microns thick attached to a microscope slide that can be examined under a polarizing microscope to identify the mineral composition of the rock.  

The process starts by attaching the rock sample to a glass microscope slide.  Below the rock is being attached against the frosted glass side of microscope slides with epoxy on the pressure jig that provides even pressure and a consistent thickness of epoxy.  If samples are very porous or crumbly, they are first saturated with epoxy, sometimes using vacuum impregnation.  There can't be any air bubbles or unevenness between the rock and the slide surface.  It takes a couple of hours for the epoxy to cure on the hotplate where the jig rests.

The next step is to cut the rock samples down as soon as possible after the epoxy sets, especially large samples as they cool more unevenly and could generate enough force to crack the glass slides.  The excess sample is trimmed neatly off with a vacuum swing arm on a rock cutting saw (below).  The glass slides provide a good seal on the vacuum plate, the arm allows the new cut to be parallel to the surface of the slide so the finished product will be exactly the same thickness all over.

Next the slides with thicker-than-final rocks firmly attached are placed on the lapping machine to be slowly polished down to the final exactly-30-micron thickness.  A vacuum system again holds the smooth glass slide against the weighted chuck, holding the rock sample down to the grinding surface.  The grinding plate has to be absolutely flat or the finished slides will be uneven so Steve constantly monitors the process, moving slides and arms around.  In the picture below you can see one vacuum chuck loaded up with slides, ready to go on the lapping disc seen behind.  Various sizes of abrasive grit slurrys are used to provide the grinding action, getting finer and finer as the process comes to a close.  Using a fine grade grit at the end is important for optical quality work.  The final few microns are polished away by hand.

Steve Petrushak is an artist and miracle worker.  Samples so crumbly that we could barely (or couldn't)

 get them out of the core in one piece, he manages to create perfect thin section slides.  The ANDRILL team is lucky to have him!  He examines each finished slide to make sure it is ready to be used to identify the core's mineral components at that sampled depth.  He has requests for 600 thin section slides this season, which works out to about 50 every two days.  He is currently managing around 15 every day so will be continuing work after some of the team has left the ice.  To work in this field he says is useful to have some background in mineralogy, optical geology, and crystallography, as well as a good mechanical feel. 

The finished product!

Eye to the Microscope

On the next microscope over, Dr. Kari Bassett spends much of her time examining and describing thin section slides like the one shown twice in different lights below (tune in tomorrow for all the details on how these thin slices of rock are made). Even though we look at them both under a microscope with different lights to learn about them, one major difference between the thin section slides and the smear slides I am working with is that the thin section is a slice of rock of known thickness - 30 microns.  Knowing the thickness of the slice allows scientists to use light accurately identify the minerals that make up the rock. A "rock" is anything made of multiple minerals. 

On the first look at a slide, the aim is to categorize the compositional type of the rock the slice was taken from (e.g. mostly terriginous) and get some grain size data.

When Kari looked at the slide above (plane polarized light on the left, cross polarized light on the right) some of the things she noticed were the two large chunks of material included in this rock.  In plain polar the one on the left is transparent and yellow, in cross polar it is black and opaque (can't see through it) - this means it is composed of glass.  How on earth does glass get into rock?  Volcanoes!  This whole area is tectonically and volcanically active.  We even have an active volcano, Erebus, on the island we are living on.  The bubbles in the glass indicate that the eruption occurred in cold conditions, the frothy lava didn't off-gas entirely before solidifying. Since it is only a small piece of volcanic glass, it has travelled to the place where it was incorporated into the sea floor.  The chunk on the right side of the slide, opaque and black in both types of light, was changed by the weathering process into pyrite or magnetite.  Overall this is an iron rich sample.

Even if you don't have one of the vital handbooks for checking on what you are seeing under the microscope, like The Colour Atlas of Rocks and Minerals in Thin Section or Microscopic Identification of Minerals, take a look at the paired images of a thin section slide below and describe features you notice.

Of the many things you might notice, look at the two grains that are brownish tan in the plain polar light on the left.  These demonstrate why mineral identification of grains needs both plain polar and cross polar examination.  When you look at the same two grains under cross polar, one is still brown and transparent, the other has turned black!  That one is glass, the other pyroxene (also a volcanic mineral).  Like the pyroxene in this slide, some minerals look the same under either light, others change a lot.  Either way, it tells us about what type of mineral it is.

What types of things can you think of that you need different sources of information about to be sure you are accurate?  What might be a good analogy for thin section mineral identification? 

For more on thin section identification, check out this online guide.

Boxing Day

Like me, you may never have wondered where all the boxes for the core come from.  They are just part of the scenery!  No one nips out to the corner store to buy them.  Today we had to build them ourselves :) 

A major part of planning for any science team heading to Antarctica to do research is figuring out to the last item what will be needed to conduct their science work for their whole visit.  There are some things that are common to all science teams that NSF brings in and maintains at Crary

 lab: glassware etc. and even some larger pieces of equipment.  For teams that require specialized 

machines, computers, tools or supplies, they figure out what and how much they will need, then pack it up and ship it to the folks at Raytheon, well in advance of deployment.  

Don't miscount - you might end up in the embarrassing position of having brought down too much or too

 little.  Too much and you wasted precious cargo space.  Too little and you might not be able to finish your science work.  Logistics pros from Raytheon schedule the cargo in and

 out of all USAP sites, planning so that the available space is used to get things there just in

 advance of when they are needed, as there isn't too much storage but the science isn't being held back either.

Box party in the lab!  Everyone comes and 

pitches in to turn huge piles of flat waxed cardboard into core boxes.  Today we made boxes for HQ (3 sections of core per box) and NQ (4 sections of core per box) diameter core.  These boxes are a little over 1m long.  This stuff is tough.  Thick waxed board has to be painstakingly bent at the dotted fold lines to make the right shape.  There is a lid, base and insert for each box.  Making boxes takes time but there is lots of teamwork and music, so we have fun.  After, we have to scrape all the extra wax off the tables and floor - not as much fun.  

This is our second box party, hopefully we won't need another before we are done.  How many boxes do we need?

Just think about this example: for 1000m (or 1km) of core, if a third is drilled in each of the 3 sizes it would make 333m of PQ, 333m of HQ, and 334m of NQ.  How many boxes would we need?  

(hint: each PQ box holds 2m of core, each HQ box holds 3m of core, and each NQ box holds 4m of core.)

Smear slides galore!

My main job with the sedimentology team for the last several weeks has been taking photographs in regular light and cross polar light (see the pictures at the bottom of this blog) of magnified smear slides from the core. Brad Field on the night logging crew makes at least one smear slide from each meter of core (we have drilled 1138.54 meters of core = at least 1139 smear slides) and more from some intervals of sediment. A smear slide is made by taking a little scrape of the sediment with a tool (toothpicks and dental tools are both used) and then spreading that sediment sample thinly on a glass microscope slide. A clear fixative is added to the slide to hold the sediment in place and then a cover slip is attached. Each smear slide is labled with the depth in the core from which it was taken.

These smear slides are used initially by the night logging crew to help with the description of the core and to give the initial compositional name to the sediments. The sediment might be mostly terriginous (sediment from the land), or perhaps have more volcanic or biologic origins. The smear slides also give the team some information about grain sizes. This may make the difference in the name given to the sediment in the formation. For example, diamictite vs sand with pebbles. To be true diamictite, the sediment must have all three grain sizes, gravel, sand and mud, without any one of those size classes, that section of rock will have another name. This information is part of Chris Fielding's core summary shared with the whole group every morning.

The photos I'm taking are primarily for archival purposes. There are scientists working with this information all around the world and most will never travel to Florida to view the actual core itself. The images taken by the teams here are placed on a shared computer drive that everyone in the project has access to. This makes sharing the samples much easier than having to physically send the one set of smear slides to different countries....it also means that we only need one set, because everyone can use it, we don't need one set for each scientist. With 1200 smear slides, you don't want to make lots of sets! It is also part of our data set, the information that core description and characterization is based upon needs to be accessible to everyone in the team.


Compare the two pictures of the same microscope view of smear slide (at 10x). What observations can you make about the various grains with the two kinds of different lighting?

Do you see what I see?

When I was in Tanzania, I found out a curious fact. When I am scanning the bush around me, I don't pick up leopards or other cats at all. I notice birds and ungulates, am often one of the first ones to see them, but a cat would have to be chewing on my leg before I can find it. Possibly this is because I spend most of my time in Alaska with half an eye on the look out for moose or bears and I am always looking for a new bird. My search image is well developed for these types of shapes and motions....but I've never spent any significant time in an area where it was important to notice large cats - or for that matter, snakes, which I've nearly stepped on at times.

Very similarly, the scientists looking at the core bring their areas of greatest experience with them when they look at the core. A volcanologist will tend to notice igneous features while, for a sedimentologist, the most obvious parts of the same section of core will be the layering and texture patterns of the grains of sediment. We all do this to a greater or lesser extent - we tend to be drawn to and pay more attention to the things that interest us most or that we are most familiar with.

One of the great strengths of the multi-disciplinary nature of ANDRILL is that everyone brings their special area of interest to the endeavor and then shares their ideas and observations with others who have very different starting points and backgrounds. The scientific discussion then involves exploring the ways in which the data might fit together to answer the big question of what was happening in this area of Antarctica in the past. The final explanation that is rendered must accomodate all data from many science disciplines, making it a much stronger statement than one coming from just one viewpoint.

The interpretation of the SMS sediment core needs scientists from both tectonic and environmental perspectives. For example, evidence in the core for deeper water environments may indicate an increase in sea level caused by ice sheet melting or it might indicate rifting and subsidence in the plates of the area - or more likely, a combination of both. We are looking in the core at a record of sedimentation and erosion. Sedimentation happens in where there is both space for sediment to accumulate and sediments in the area to fill it. We need a complete picture of both the tectonic and environmental factors that might be creating the sediment and space for it to fill in order to understand what was happening here in the past.

Take a look at the picture at the top and see what animal you notice first (there are two). What are the things you focus on in an outdoor environment, what do you see first? How about in indoor environments? How does what you notice differ from what someone else in your school or family notices?

ANDRILL Open House

I took this photo of the Ross Island cable TV channel that posts activities in McMurdo. As you can see, all the folks involved with ANDRILL hosted an Open House for the greater community to attend. It was a really great event. As one of my fellow ARISERS said, people appreciated the enthusiasm the scientists had for their particular area of expertise.

We teachers staffed the meet-and-great area of the open house where we shared activities that can, or are used in schools with students. Most of the activities we used were developed by LuAnn Dahlman, an ARISE teacher from last year as part of her Flexhibit. Thanks LuAnn

In the photo to the right, you can see some special people using the core drilling model Joanna and I put together to demonstrate the actual drilling process. The gentleman on the left is Dr. Peter Webb. He first started coming to Antarctica as a geology student mapping the area know as Wright Valley (I hope to be taking a field trip out there in the next couple of weeks) and has been a leader in geology research here ever since. You can learn more about him, his early adventures and the science he is still doing by viewing Megan Berg's latest video (video #3) at www.andrill.org/iceberg. The woman interviewing him is Moira Rankin who produces stories for Sound Print Media. Her stories are picked up by some NPR stations. Her sound technician is Jarred.

Once a group of ten or so guests had assembled, ANDRILL scientists and staff led visitors on tours of the labs to see all the work that is being done as part of this very complex project. In this photo, Dr. David Harwood is getting a group together for a tour. We had some great feedback from some of the 150 or so guests that it was a tremendous afternoon. I wish everyone I know could have stopped in too.

Tools of the Trade

The science teams here use lots of different tools while examining the core, some simple, some very complex. By far the most commonly used items are magnifying lenses of all types and lab or science notebooks. White wax pencils, probes and flags are all used to mark the core, and meter sticks are used to find the precise location of a sample.


Besides the already described tools used by the curators to take samples (see Core Curating, Nov 9), lots of smear slides and thin section slides are made from samples of the core. Smear slides involve scraping a tiny bit of sediment from the core with a pick and spreading it very thin in water on a glass microscope slide. Thin sections are a very thin slice of rock attached by strong glue to a glass microscope slide and then ground down until there is barely any left. Many specialized tools are used in this whole process (more details to come in a future blog!) including the one shown here, pressing the rock onto the slide as the glue dries to make an even bond. Once we have all these slides, we need lots of microscopes to look at them.

One very important tool we use to gather data is the high quality scanner that takes a very detailed picture of the face of the core once it is split. This information is entered into a computer program called Corelyzer that everyone can access. We have lots of computers and our own ANDRILL drive that everyone can access and upload information to share. Another important computer program used is PSICAT- it creates a graphical record of all the core characteristics as they are logged, cm by cm.

There are other scanning machines that don't take pictures but instead make measurements of various features of the core. This one, at the drill site, measures the core density, its velocity (how quickly a sound wave travels through the core), its infrared emmissions, and magnetic susceptibility (how magnetized the core is in response to a magnetic field).

What tools do you use on a regular or daily basis? What specialized tools do you use for a particular purpose? Are there tools that would be useful to you that you do not have?

Snow Day from 11/08/07

Snow Day- 11/8

The weather wasn’t very good for doing science yesterday. The crew went out for a bit, but had to come back to came when snow started to fall making visibility a problem. Dr. Marv Speece entertained us in the afternoon with a lecture on geophysics. We went to bed last night with fluffy snowflakes falling through still air. Sometime around three this morning the wind started howling so that the tents were all flapping frantically. Needless to say, no data collection again today. It’s hard to tell if it’s currently snowing or are the 20+ mph winds just blowing the fluff that fell yesterday. Current temperature is around 17F, positive numbers thank goodness. Anyway, it’s hard to see much except shades of white and gray, and even more difficult to function outside for very long.

Our chief, Dr. Ross Powell, Glacial Sedimentologist from Northern Illinois University, continued our lecture series on glaciers in the science tent. Ross first visited Antarctica in the 70’s as a graduate student and has been here numerous times since then. He’s been particularly interested in the Mackay glacier over the last ten years and is very keen to get some good sediment records showing up on our seismic survey. On days that we’re working at the survey site, his primary responsibility is supervising the data collection process and pondering the great complexities of glacier behavior.

Today’s lecture focused on different types of glaciers, their behaviors and sediment records based on climatic differences, and how that all relates to future climate changes. I asked Ross to explain what we’re all doing here in Granite Harbor and gave him a two paragraph maximum.

Ross says, “On the continental shelf around Antarctica are some very deep troughs and basins that were scoured and eroded out when the ice sheet was much larger and expanded over those areas. Since the ice sheet last started to shrink and retreat, some of those troughs and basins, which can reach over 900 meters below sea level, have been special repositories for marine sediment. Ocean currents have carried and concentrated sediment in the basins so that it accumulates very rapidly, at a rate of several millimeters every decade. Because these basins have been exposed and have been receiving this sediment over the past 20,000 to 7,000 years as the ice sheet retreated and opened-up the continental shelf, thick accumulations of these geologically very young sediments has been stored in the basins, some now reaching up to 200 meters thick. These thick piles of sediments are made mainly of the remains of marine plants or algae named diatoms that form the basis of the food web in the highly productive Southern Ocean. These marine plants need sunlight and a good supply of nutrients from the water to flourish; some even like living in sea ice that forms every winter around Antarctica by sea water freezing. Nutrients are best provided by strong winds blowing across the water surface causing deep waters that carry the nutrients to rise up to the surface where the diatoms live.

What we want to do is core one of these types of sediment records that now lie at the bottom of the Mackay Sea Valley, and look for periods of time in the core when diatoms were flourishing and when they weren’t, going back over the last 7,000 years. Other types of sediment accumulate when diatoms are not abundant, because waters are either less nutritious or perhaps were covered with very thick sea ice cutting down on the sunlight reaching the upper seawater layer. These types of records can tell us a great deal about the ocean circulation changes over time, which we want to understand, and compare those changes in Antarctica with what has happened in lower latitudes such as around New Zealand and even in tropical waters closer to the equator. We need to understand how these ocean waters in different areas of the world are linked to each other, so we can better predict how they may change as global warming continues. It is especially important for Antarctica because of the possibility of all of its ice melting as Earth continues to warm.”

Thank you very much, Ross!

Diatom Ice

It's the afternoon of November 13th. I'm back in McMurdo and very happy to finally post blogs I wrote last week. This is one is from November 3rd.

So, I noticed when we first started shooting off the air cannon to conduct the seismic survey, some of the ice that came up with the sea water and air bubbles looked it was formed from root beer. Here’s a more scientific description: irregularly shaped chunks of translucent ice ranging in size from approximately three to eight inches in length with mottled internal yellowish brown coloring. I know from the scientists here with ANDIRLL that the coloring is colonies of diatoms. Diatoms are plants that are about the size of the head of a pin and are made of silica (a sand-like substance). Most of the diatom ice slides back into the hole with the receding sea water when the air gun ceases firing. Hopefully, the diatoms go on living and no harm done.

One morning when we arrived at the survey line to begin our day, I noticed a chunk of diatom ice on the surface of the area of the last hole we shot from the afternoon before. It had sat out in the bright sunshine all night. Instead of the usual brownish color I’ve become used to, it was a lovely shade of green. I took a photo of it lying on the aqua colored sea ice with the toes of my “bunny boots” (seriously, that’s what these boots are called-why, I don’t know!) to prove to everyone that Antarctica isn’t only shades of white.

Here’s a science question for you; why was it green now and not still brownish? Why is that important? To test my hypothesis of why that happened, I collected some other pieces of brown diatom ice and left them out in the sun by the last hole of the day. My prediction was that they would be green the next day. My prediction was correct. When we came back the next morning they were green. For comparison I collected another piece of brown diatom ice and photographed them next to each other. The brown ice is the piece on the left.

So, what’s happening with the diatom ice? And why is it important?

Who (or What) Goes There?

A couple of evenings ago I went for a walk out to Hut Point with Robin. It has been very windy over the past couple of days, and yesterday it was gusting upwards of 40 knots; it was ‘Condition 1’ at several locations out on the sea ice / ice shelf yesterday - see the McMurdo weather information page below:

If you look at the picture below you will see what we saw in the snow around the Hut.

You can see that the footprints left by previous walkers after the most recent snowfall have been preserved, but you will notice that they are standing up above the surrounding snow. Why is this? Well, when we step on the snow we press down on it, this pressure forces the snow crystals to bond together. When the wind picks up, it will blow away the looser snow that has not been stepped on, but the wind is unable to pick up and move the snow that has been bound together in the area of each footprint. Hence the footprints that were formerly depressions in the snow are now sticking up above the remaining snow. This picture is taken looking approximately to the west – what direction was the wind coming from? Which direction was it blowing towards? So we have clear evidence for people walking around the hut. What else could we do to try and figure out who it was that was walking around the Hut?

The picture above is the view looking towards the north-northwest from the Hut. In the foreground you can see pressure ridges that have built up in the sea ice. On some of the warmer days about a week ago some of the ice melted at the surface, forming melt pools; this water has since refrozen.

Tonight (which is Tuesday) some of us are going over to Scott Base (see picture above, taken a couple of weeks ago) for dinner; they have a superb view of some pressure ridges there [note added later: we just got back from Scott Base; we had a wonderful dinner, with great company - the Kiwis had been watching the Melbourne Cup on TV -it is the Australian equivalent of the Kentucky Derby. However, we could not see much outside because the weather had deteriorated to a Condition 2].

The footprints we saw near the hut have a subtle link to some of the features we are seeing in the core. There are places where the sediment we see in the core is disrupted in a way that indicates some kind of bottom-dwelling organism was foraging for nutrients. When these critters leave distinct patterns behind in the sediments, the patterns are called trace fossils. You are probably familiar with the use of the term fossil for remains of harder parts of plants or animals (e.g. shells and bones), which are called ‘body fossils.’ The term Trace Fossil refers to marks or tracks in sediment that result from some behavior by an animal that provides some evidence for the shape and characteristics of the animal. There is, in fact a whole branch of Paleontology (the study of fossils) devoted to the study of trace fossils; it is called Ichnology. The word Ichnology comes from a greek word ‘ikhnos’, which means ‘trace’ or ‘track’. The traces left by various critters are divided into groups that indicate what the critters were doing, i.e. burrowing, boring, footprints, track marks, feeding marks, trails. Trace fossils are tricky to identify in the core, but some of the fossil material we are seeing in the core includes material that looks like this (the creamy white tubes - the picture is about 4 cm wide):

The little white tubes are actually the ‘burrows’ made by serpulid worms; the insides of the burrows were coated with the white material, which is actually a kind of outer shell made by the worm. These worms are quite unusual.

Lets look at some fossils from elsewhere (i.e. NOT in the core, or in Antarctica); the picture here is of some dinosaur footprints; these trace fossils make up a trackway.
The picture below is of human footprints from Laetoli in Tanzania – they are footprints of early hominids. They have been interpreted to record the hominids fleeing from a volcanic eruption. These are Trace Fossils – they are a type of trackway.



Links and Teacher Resources on Trace Fossils
http://museum.gov.ns.ca/mnh/nature/tracefossils/english/index.html
Site has nice simple definitions and some K-12 teaching ideas and activities

http://en.wikipedia.org/wiki/Trace_fossil
General Information and links on Trace Fossils

http://education.usgs.gov/schoolyard/fossils.html
Information and Classroom Activities involving Fossils

http://geology.er.usgs.gov/paleo/
USGS Website with Fossil Information

http://www.palaeos.com/Palaeo/TraceFossils.htm
General Information on Ichnology

http://www.envs.emory.edu/faculty/MARTIN/ichnology/
A Guide to Ichnology from a Specialist

http://hoopermuseum.earthsci.carleton.ca/10.html
Guide to Trace fossils from the Hooper Virtual Natural History Museum (Carleton University, Canada)

http://hoopermuseum.earthsci.carleton.ca/2001_tracefossils_dr/webpages/coprolites.htm
Information on Coprolites on Hooper Virtual Museum Page

http://www.geo.ucalgary.ca/~macrae/t_origins/carbbones/burrow.html
University of Calgary – Information on Trace Fossils

http://www.trilobites.info/trace.htm
Information on Trilobite Trace Fossils

Fracture Factory

With the pressures exerted on the core sediments during drilling, transport and splitting, it is not surprising that there are many cracks and breaks in it. Fractures caused by these processess are classified as drilling induced. There is a team of scientists at the drill site logging (recording) all the fractures in the core, but they are primarily interested in natural fractures. Natural fractures are those created by tectonic movement within the earth's crust or stress on the rocks caused by changes in loading (something heavy above the rock pressing it down - in this area it is usually a volcanic or glacial "something").

Cristina Millan helped me understand some of the different kinds of fractures I have been seeing in the core. She is one of the scientists logging fractures in order to understand the pressures acting on the crust in this area over time.

All of the open fractures are recent in origin - induced fractures. One common type is a tensile fracture, where the pressure experienced by the rock causes two parts to separate. This usually causes a crack straight across the core. We see LOTS of this type of fracture. A second type of induced fracture is a petal centerline fracture. It is caused by the drilling process. This type of fracture has a curved shape coming in from the edge of the core and then makes a straight line down the core. Another common fracture we see happens when rock that is not strong is split in half, creating breaks along weak points and a puzzle or mosaic appearance.

Natural fractures are generally not open or fresh, they are often filled in or mineralized. The most typical natural fractures are veins and faults. Although veins can be broad, in the sediments we are seeing in this core, veins are quite small. The material that fills the fracture to create the vein is usually a different color than the surrounding sediments, making its angled line travelling through the core more visible. A vein usually has a very characteristic angle (or dip) in which they incline through the sediment. Tensile fractures may sometimes occur on vein fractures as the mineralized vein is a weaker point in the core.

Faults are also natural fractures. They are identifiable because some sections of layered sediment will have been shifted up or down or around and appear out of place with the surrounding pattern of layering. The process of fracturing within the rock doesn't remove sediment, it just moves it around or creates spaces for mineralization.

Look at the pictures on this section and see how many of the different types of fractures you can identify.