How to properly dissolve matrix to reveal microfossils? Tips & tricks needed

[ziggycardon]

Hi, 

a few days ago I went on my first ever fossil hunting trip to Eben-Emael, a Limestone quarry in Belgium that dates to the Maastrichtian and is part from the type location (the historical ENCI quarry being only a 3,5 km to the north.

The trip was orginized by the BVP (Belgische Vereniging voor Paleontologie) and a short report of the trip with phot's and some of the finds can be found in this topic by @Manticocerasman who I was lucky enough to tag along with, cause I doubt I would have found many mention worthy fossils without the guidance of Kevin.  

 

But since I am into microfossils I decided to collect some samples of the limestone without the obvious fossils home to later be able to look for microfossils as it should be quite rich. I think I have around 1 - 3 kg of matrix left to look for microfossils. 
But I have never myself dissolved matrix, and although it seems easy, I don't want to make any mistakes.
During the trip they advised me on two different approaches, depending on what kind of fossils I wanted to find.
One approach was dissolving in water and the other in vinegar, but now the seeming obvious question. How exactly do I do that?

Should I just take a bucket of a glass, fill it halfway with said liquids and just wait? Or should I use a sieve and lay the block there so only fossils remain in the sieve and the rest goes to the buttom. Does the limestone just dissolve or does some kind of putty residu where the microfossils will be in? If so, how to properly remove the fossils when you pour out the liquids without pouring out the fossils?

I know I have many questions and some might be very obvious and straigh-forward, but I really haven't done this before and I would like to do it the right way from start.  
So thanks in advance for any tips & tricks, I would really appreciate any help! 

[Al Dente]

If you use vinegar or other acid, you will be left with phosphatic or quartz fossils and most other fossils will be dissolved. I would recommend trying water first. Dry the matrix completely in an oven and then place it in water. This may or may not result in the matrix breaking down. If this doesn't work, there is a method using "Glauber salt". Here is a method described by Andrew Gale in one of his Roveacrinoid papers.-

 

"Material from the English chalk was obtained by processing with Glauber Salt (anhydrous NaS04), using a technique modified after that of Surlyk (1972). 1kg of fragmented chalk sample (pieces about 5-10cm diameter) was dried in an oven at 60oC for 48 hours, then soaked in a saturated solution of Glauber Salt, obtained by dissolving powder at 30oC in tapwater. After 30 minutes, the excess solution was poured off, and the chalk was frozen for 12 hours in a domestic freezer. The thawed chalk was screened in a 425 sieve, thoroughly washed, and then dried at 60oC. The residue was placed in a saturated Glauber Salt solution and frozen again. The process was repeated until the fossil fraction was clean and the fine particulate chalk significantly reduced in volume. This method has some advantages over the standard technique; although it uses more Glauber Salt; the smaller residues are easier to handle and require less space, and an assessment of the degree of breakdown and cleaning can be more readily assessed. With really fragile fossils, like roveacrinids, fewer cycles of processing are preferable."

[ziggycardon]

1 hour ago, Al Dente said:

If you use vinegar or other acid, you will be left with phosphatic or quartz fossils and most other fossils will be dissolved. I would recommend trying water first. Dry the matrix completely in an oven and then place it in water. This may or may not result in the matrix breaking down. If this doesn't work, there is a method using "Glauber salt". Here is a method described by Andrew Gale in one of his Roveacrinoid papers.-

 

"Material from the English chalk was obtained by processing with Glauber Salt (anhydrous NaS04), using a technique modified after that of Surlyk (1972). 1kg of fragmented chalk sample (pieces about 5-10cm diameter) was dried in an oven at 60oC for 48 hours, then soaked in a saturated solution of Glauber Salt, obtained by dissolving powder at 30oC in tapwater. After 30 minutes, the excess solution was poured off, and the chalk was frozen for 12 hours in a domestic freezer. The thawed chalk was screened in a 425 sieve, thoroughly washed, and then dried at 60oC. The residue was placed in a saturated Glauber Salt solution and frozen again. The process was repeated until the fossil fraction was clean and the fine particulate chalk significantly reduced in volume. This method has some advantages over the standard technique; although it uses more Glauber Salt; the smaller residues are easier to handle and require less space, and an assessment of the degree of breakdown and cleaning can be more readily assessed. With really fragile fossils, like roveacrinids, fewer cycles of processing are preferable."

Thank you for the fast and detailed reply.
It is definiatly helpfull, I will first try water as it seems like the safest method.  
Thank you for your help!

[Mediospirifer]

Let me say first that my methods are probably not standard, but they work. I figured it out as I went along, with help from the Forum. That said, here's my suggestions.

 

First, whichever method you use, step 1 should be to break it down into small pieces. I'll put my rocks into a canvas bag and whack it with a chisel and  sledgehammer. This does damage the bag, but my goal is to keep the chips that would otherwise go flying.

 

Also, whichever method you use, you have the same final step of sieving the residue and catching it in a filter. I like to swirl the residue-bearing water a bit (to disperse the particulates and make the water cloudy), wait a few seconds (for the larger ones to settle), then pour off most of the muddy water until my particulates mostly settle out quickly. This takes a few repetitions.

 

Do you have a set of soil sieves? If so (unless they're made of cardboard or something else that shouldn't get wet), you can pour the water-bearing residue through the whole stack (coarsest sieve on top, finest on bottom). I'll use a dishpan to catch the water at the bottom if I want to look at the residue that passes through all of them, but don't usually bother (My smallest sieve is a #200. That's tiny!) I'll also immerse the sieves one at a time (in a dishpan, keeping the top out of the water, submerging the screen and particulates)starting with the top one, and swirl them a bit to encourage smaller bits to go through, then pour off the rinsings into the rest of the stack. Repeat for each sieve.

 

For catching the residue, I use a coffee filter in a colander. They work quite well--I've poured limestone residue-bearing water into a coffee filter without first pouring off the finest fractions, and observed what looks like mudwater going in, and clean water coming out! This leaves a filter full of mud (which will clog the filter and slow it's progress). The mud is hard to work with if you haven't separated the fines.

 

As far as using vinegar goes, I've had fairly good results there. I put as many rock chips as will fit into a small plastic container (500mL), then pour in as much vinegar as will fit with a lid. Cover it loosely, and let it stand until the effervescence (bubbling) stops (usually overnight). The visible difference after one soaking will be that there is some muddy residue in the bottom. I'll always pour and sieve the residue, and rinse off the rock chips, before setting the rocks to soak again. For larger chunks, I'll use a soft natural-fiber paintbrush (small!) to help remove the residue that sticks to the rock.

 

I've seen a suggestion that putting the rocks into a basket that nests into my vinegar pot might speed up the rinsing process, but I haven't tried that yet. That seems like it would work well for the smaller chips.

 

Vinegar is good for extracting phosphatic fossils (teeth, scales, etc.), but if you have too much it can dissolve those too. I'll use as little vinegar as I can to cover the rock, in the smallest container possible. And I wash the fines with several changes of water during the filtration process.

 

Good luck, and have fun with your explorations! Just remember to be patient. Neither of the techniques described here (so far) are quick.

 

[ziggycardon]

Thank you very much for sharing, sounds like it's a really good method so I will definiatly try it out!