Miatria Posted March 12, 2016 Share Posted March 12, 2016 Has anyone dissolved the calcified outer surface of a fossilized coral head to reveal the agatized coral underneath? If so, how? Wondering about using acids? Zookeeperfossils.com Link to comment Share on other sites More sharing options...
Mediospirifer Posted March 12, 2016 Share Posted March 12, 2016 My experience with using acid with fossils is limited to dissolving matrix to get the microfossils (I use ordinary vinegar). I wouldn't recommend it for the purpose you're describing. The acid will attack all exposed carbonates, and depending on the composition of your coral may leave you with a pile of sand! If the core is truly agate, it will strip off all of the carbonates and may leave you with a heavily pitted specimen. Not that the agate will dissolve, but you really can't tell how the boundary between agate and calcified area is structured before removing the outer area. Personally, I polish coral pieces to reveal the structure. Someone with more experience at prepping may have other techniques. I have considered (but not yet tried) soaking a cut slab of limestone coral in vinegar to see how the surface etches. I'm curious as to whether I can duplicate a weathering effect on one piece of coral my husband and I collected, where the internal coral structure stands in shallow relief. I don't plan to etch it too deeply as it's solid limestone. In my weathered piece, it's the coral skeleton that has weathered away, leaving the internal casts showing the structure (Hexagonaria from Columbus limestone). If you want to experiment with vinegar, be aware that it's a slow process. I let my pots stand for a couple of days when etching for matrix, then change the vinegar for a fresh batch. The rock doesn't show much change after a single soak, it takes several to significantly reduce a rock to matrix residue. I hope this is helpful! Link to comment Share on other sites More sharing options...
Sacha Posted March 13, 2016 Share Posted March 13, 2016 Aimee, I have not tried acid on coral. However, judging buy the hardness when cut and polished, I think the rind is not a residual limestone crust (at least on mine), but a porous silica based layer. You can try vinegar straight to see how much it foams, if any, and if it does then let it go as long as you want because the agate will be fine. If the rind remains, then give up the chemical approach because you'll need pretty nasty stuff to go on from there. You can try a variation on tumbling with grit, depending on the size of the heads you're doing. If yours are baseball size or smaller, I'll try a couple for you. Link to comment Share on other sites More sharing options...
FossilDudeCO Posted March 13, 2016 Share Posted March 13, 2016 ......If yours are baseball size or smaller, I'll try a couple for you. Baseball size or smaller? How big do some of these corals get John? Link to comment Share on other sites More sharing options...
Sacha Posted March 13, 2016 Share Posted March 13, 2016 Baseball size or smaller? How big do some of these corals get John? Two to 3 feet across at the very least Blake. Usually the big ones are poorly agatized but frequently they are hollow and botryoidal. I donated my biggest and best one to the Daytona Museum of Arts and Science last year. This isn't a great picture of it, but it was about 24"x18"x18" and was completely hollow with nice red/amber agate inside. This is one of the trips I sank my kayak. Link to comment Share on other sites More sharing options...
FossilDudeCO Posted March 14, 2016 Share Posted March 14, 2016 That....is....amazing..... VERY cool piece!! Link to comment Share on other sites More sharing options...
vonfatman Posted March 27, 2016 Share Posted March 27, 2016 I bet you sank your kayak! Very nice. Bob Link to comment Share on other sites More sharing options...
Recommended Posts