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Microfossil Matrix "how To" Article


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If anyone has any suggestions or corrections, please let me know! I'm looking to publish this article in our HGMS newsletter for next month.

Collecting Microfossil Matrix

Collecting microfossil matrix is the most efficient way to collect small fossils, which are often the most abundant, most diverse and best preserved fossils at any given site. Microfossil matrix is the strata out of which we often collect our small fossils. Microfossil matrix collecting involves collecting this raw fossiliferous strata in bulk, breaking it down, cleaning it, and grading it for sorting, so that it can be easily searched for fossils.

Microfossils defined:

Generally, these are fossils 10mm or smaller. These fossils will generally fall through a screen with 1/4" holes or larger, which means that they are often overlooked when surface collecting or lost when sifting. Many of these fossils can be seen by those with good vision without the aid of a hand lense; however, a microscope will open up a whole new world of fossils.

Where to find microfossil matrix:

Most fossil sites have microfossils, but most often the most abundant microfossils are found in aquatic/marine deposits, which Texas is incredibly rich in. Anywhere you find small fossils is a good place to collect matrix for processing. If you cannot collect your own, there are places online, such as ebay, where you can find microfossil matrix for sale.

Tools Needed/Recommended:

You will need a good set of tools to properly collect matrix. You will need something to dig or scrape up matrix, something to sort matrix, something to carry matrix with, and something to transport matrix home with.

To dig with:

Vigoro Dig Ez Mini Pick is my #1 recommendation, but here are others if you cannot find this one. Any one of the below will serve you well as a digging implement; it's very rare that I need any heavier duty tools than my hand pick.

V&B Manufacturing

Groundbreakers 864-03

Mini Planter Pick


Vigoro Dig Ez Mini Pick with 16 in. Fiberglass Handle

Model # 1114100

Store SKU # 656089


Hand Mattock, Feather Weight Mini Pick Garden Tool


Kusakichi Brand #11 Pick Hoe


To carry your matrix:

Often times you will have to park a little ways away from your vehicle. Dirt is Very Heavy (usually between 8 and 15 lbs a gallon depending on the type), so I would recommend that you get a good, comfortable hiking backpack Without zippers for hauling your matrix. I would highly recommend a 20-30 liter backpack. I hauled 5 gallon buckets when I started out, but using a backpack is tremendously easier and safer (I use a 30 liter, which carries 8 gallons--I do recommend a 20 for starting out). If you get a zippered backpack, the zippers will quickly become clogged with dirt and will eventually fail. As heavy as dirt is, you want something made to take the weight and easily carried without breaking your back. As a side note, you may want to line your backpack with a trash bag to keep it from getting so dirty.

To store/transport your matrix:

I recommend a regular 5 gallon, $3 bucket from walmart or home depot. Make sure to buy a lid and duck tape to seal each bucket, otherwise, they can dump over in your car, spilling fossils and dirt all over your interior, which has happened to me before. Also make sure to strap in or otherwise well secure your buckets. If you were to slam on the brakes, would a bucket come flying forward?

To sift matrix onsite:

In many cases, you want to remove any large rocks from your matrix in order to maximize your end yield. Rocks only take up space, so it's best to get all of those out that you can. For this, I usually use a two part sifter using 1/2" and 1/4" wire mesh. The 1/2" mesh removes large rocks and large clumps but rarely catches any fossils. The 1/4" will catch larger fossils, which are easily picked out to take home, while allowing your microfossil matrix to pass through. I use a "bucket sifter", which I can sift over a 5 gallon bucket and then pour into my backpack.

Collecting Methods:

When I arrive onsite, I first scout the entire exposure to see where the highest concentrations of small fossils are. I look for loose fossiliferous material that can be broken down with water or H2O2, although there are also methods for breaking down harder material involving vinegar, boiling, chemicals, and freezing. I look for the most concentrated locations and either surface scrape with the flat end of my tool, which is the least invasive method, scoop up gravel if in a creek, or I collect chunks of fossiliferous strata. In any case, I do not pothole or tunnel, as this is one of the reasons fossil collectors are banned from many sites. If the matrix is from a creek or loose surface material that I scooped/scraped up, I will sift out anything larger than 1/4" and pour all the smaller than 1/4" material into my backpack to hike out. If the matrix is taken directly from strata in chunks, I will usually just dump the entire chunks of matrix into my backpack.

If you are lucky, you can sometimes find red harvester ant beds (Pogonomyrmex barbatus), in which case the ants often times will collect microfossils while burrowing (they move any rocks in their way while digging) and will dump them at the surface. If you do collect from red harvester ant beds, be Very careful to remove no more than 5% of the mound, from the outermost perimeter of the mound, or you may very well kill the entire mound and all of your tiny fossil sorters. It's also not a bad idea to feed them if you are so inclined.

After I have a full backpack of matrix, I hike it out to my car and dump it in 5 gallon buckets to transport back home. I use a rubber mallet to fully seat a lid on each full bucket, then use four 5" vertical strips of duck tape to secure the lid. There's nothing worse than having a bucket full of matrix to dump over in your car. I also line the back of my car with a plastic painters sheet ($1 at walmart or home depot) in case any matrix does happen to spill in my car or in case the bottom of the buckets have mud on them.

Processing your matrix:

After you bring your matrix home, it needs to be processed to both concentrate your matrix and to clean the fossils in your matrix so they can be easily picked out during sorting. Some matrix can just be washed and then dried, such as river gravel, but others need to be broken down with water or with hydrogen peroxide. For clay based matrix, I highly recommend first allowing your matrix to fully dry in the sun, then soaking in hydrogen peroxide, which most stores carry in the pharmacy section for $1 a bottle. Usually it takes 1-2 bottles per gallon. You want to soak every bit of your matrix and you will know this is achieved when the peroxide begins to pool on top and the matrix will not absorb more. The peroxide (H2O2) will soak into the pores of the clay and will break down into oxygen and water, expanding and causing the clay to practically dissolve, while not damaging your fossils. Leave the peroxide to soak for about 15 minutes and then fill your bucket or other container to the top with water and leave to soak for an hour or more. It doesn't hurt to stir gently to make sure all matrix is soaked. Many non-clay matrix types can just be soaked in water over night to be broken down.

After your matrix is fully broken down, you need to wash it. I will usually use a large plastic tub, in which my sifter will fully rest in, to process matrix. If you have already sifted your matrix past 1/4" wire mesh, use a screen with 2mm mesh (window screen/bug screen mesh) that is in a rectangular shape. Fill your tub half way with water and lay your sifter perpendicular over your tub so it rests over the water. Pour some matrix "mud" onto the screen, then take your sifter, turn it parallel so it can rest in the tub, and dip it slowly in the water multiple times to "water sift" until you see that all the mud is washed out. Do this for all your matrix as it is far less harsh on your fossils than dry sifting. Then lay your screen(s) somewhere where it (they) can dry in the sun. Usually concrete or rocks are best. The mud that is left at the bottom of the tub can be sifted with much finer mesh screens if you wish to look for "true microfossils" that can only be seen with a microscope. If you did not pre-sift your matrix before washing, wash over 1/2", 1/4" and 2mm mesh in the same fashion, then dry in the sun.

After your matrix is fully dry, pour your screen over a large sheet of paper, plastic, or cardboard into an aluminum pie pan or other container. When you pour matrix off of a screen, much of the smaller matrix will now fall through and can be caught and saved with a sheet of material underneath. You can now sort your processed matrix, or grade further for easier sorting using a sieve set.

Mounting/Displaying your microfossils:

There are a plethora of ways to organize and display your microfossils. In the lab, I used to take small 2ml glass bottles with corks, stick a pin in the bottom of the cork, and mount each fossil with dental wax on the pin head, then paint the top of the cork with white paint and mark with a catalogue number. At home, I either use gem jars with foam inserts, labeling each jar on the bottom, or small riker frames with foam inserts, You can also glue your fossils using water soluble elmers glue to graphing paper mounted on cardboard. Anything used for mounting gems can usually be used for mounting microfossils as well.

Cataloging your microfossils:

As with all fossils (especially with microfossils), site information is paramount to both the scientific and monetary value of your microfossil collection. I always record the GPS coordinates (I use a free app on my iphone called "commander compass") of each site, along with the county, closest town, state, date the material was collected (in case the site is destroyed later on), and later with the formation and age after I've researched the site.

Some places to start collecting microfossils:

To start collecting microfossils, try one of the two locations below.

Whiskey Bridge

Stone City Fm. Matrix

Location: Brazos Co./Burleson Co. line, Texas

Age: Middle Eocene


​​Fossils You can Find:

​Lots of shells, turritella corals, bryozoa, fish otoliths, possible shark teeth but rare

Mineral Wells Fossil Park

Mineral Wells Fm.

Location: Mineral Wells, Texas

Age: Carboniferous (Pennsylvanian)

~323-298 MYA

​Fossils You can Find:

Crinoid stems, brachiopods, mollusks, bryozoans

  • I found this Informative 6
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Very interesting and informative.

Do you use H2O2 to clean all your fossils or just the microfossils in clay?

...I'm back.

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I tried using ultrasonic bath with water to shake loose matrix apart for microscopic analysis. It worked pretty well for some materials and not at all for others. The nice thing about using the ultrasound was that it has no caustic effects of the microfossils.


Edited by tmaier
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Do you know of any specific locations within Utah or Wyoming?

Each dot is 50,000,000 years:



                                                                                                           Ꞓ.OSD.C.P.Tr.J.K..Pg.NgQ< You are here

Doesn't time just fly by?


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I use h2o2 to clean most but my pyritized fossils. It is excellent for microfossils though since you can't easily use a brush on microfossils, especially in mass quantities.

I don't know of any locations in Utah or Wyoming, but if you find any, please let me know! If you have any papers that specify localities, I can usually track those down as well

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I will let you know what I dig up (pun intended :) ) on this subject.

Each dot is 50,000,000 years:



                                                                                                           Ꞓ.OSD.C.P.Tr.J.K..Pg.NgQ< You are here

Doesn't time just fly by?


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Very good description for soft clay matrix, but what do you do when the microfossils are in limestone or another hard matrix?

Use something else :D I got some Triassic material from South Wales and spent a year and a half dissolving the matrix in dilute formic acid to get a few bone fragments and mammal teeth out. You need to experiment a bit just don't do anything too drastic.

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Use something else :D I got some Triassic material from South Wales and spent a year and a half dissolving the matrix in dilute formic acid to get a few bone fragments and mammal teeth out. You need to experiment a bit just don't do anything too drastic.

Thanks Taogan. I use anything from vinegar essence to sulfuric acid. I was just wondering if silverphoenix was going to work that subject into his article as well.


Greetings from the Lake of Constance. Roger


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  • 2 months later...

Thank you so much. This is exactly what I was searching for. After getting interested in fossils in the shale, limestone, etc. in Iowa and dealing with larger fossils, I was at a loss as to what I should use for the buckets of matrix I brought home from Whiskey Bridge. I have several large bottles of H2O2 that I got specifically for fossils but have never had to use it. However, I knew all the tools and chemicals I'd been using previously were worthless for this project. For the matrix I have already processed I just used dish detergent and water, but I was unhappy with the progress I've been making. I'm about to go see what I can find now. Thanks again!

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