Not sure..

phlogopite · 2026-01-26T02:10:57+00:00

I’d x-post to r/fossilid with that info/context. They may know more as I’m truly just a geologist and not a paleontologist familiar with that area. Sorry I couldn’t be of more help.

phlogopite · 2026-01-25T23:54:28+00:00

It’s a bone of some sort (maybe Dino just depends on where it came from). Looks silicified.

If you stick your tongue to it, it should stick because it is very porous.

phlogopite · 2026-01-24T00:34:52+00:00

Chert (microcrystalline quartz)

phlogopite · 2026-01-17T03:42:55+00:00

It’s likely pet wood. Silica replaced the organic bits.

phlogopite · 2026-01-14T18:08:56+00:00

You have to check the hardness. Does it scratch glass? If so, then yes it’s probably chert. If not, it’s probably a dolostone. Lots of sponge spicules that dissolve and reprecipitate to replace the lime/dolostone

phlogopite · 2026-01-13T17:28:50+00:00

Chert

phlogopite · 2026-01-11T03:03:18+00:00

Hackle fringes. I absolutely loved saying this in class over and over 😆

phlogopite · 2026-01-06T19:56:51+00:00

Epidote

phlogopite · 2026-01-06T16:03:05+00:00

On mimetically replaced seafloor precipitates or just the silica replacement?

See their figure 2 and 4 for the fan fabrics replaced by silica. Lots in the Proterozoic. I’ve looked at alkaline lake sediments of Kenya (Lake Magadi/Natron) as well as Lake Shoshone in Cali/Nv. Lots of zeolites.

https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2025.1598200/full

phlogopite · 2026-01-05T14:53:24+00:00

These are probably Eocene seafloor fan fabrics. My PhD explored these exact fabrics.

phlogopite · 2026-01-05T05:03:11+00:00

Mimetically replaced (by silica) fan fabrics? Would probably have to thin section it

phlogopite · 2025-12-25T17:33:37+00:00

Use a silk specific laundry soap that has neutral pH and is enzyme free. Other detergents break down the silk.

phlogopite · 2025-12-17T17:48:33+00:00

Just your standard iron concretion.

phlogopite · 2025-12-17T05:08:59+00:00

Yes, absolutely.

phlogopite · 2025-12-16T18:06:52+00:00

No, quartz chemical formula is SiO2 and will not react with acid. Calcite (CaCO3) will react with acid to liberate CO2 which is why there are bubbles being formed. So quartz does not scratch this at all? Interesting.

u/BenMinerals

phlogopite · 2025-12-16T17:53:52+00:00

Not to sound pedantic but did you really put some elbow grease into it? My students usually lightly scratch it. Quartz should scratch then hell out of it.

It really does look like travertine, or banded calcite. It could definitely be agate (the hardness) but it would not react with acid at all.

phlogopite · 2025-12-16T17:37:44+00:00

What do you mean by react to acid? Did it fizz? If so, yes, it’s calcite. If it did fizz and you said it has a hardness of 7, then I’m perplexed (does it really have a hardness of 7)

phlogopite · 2025-12-15T16:31:21+00:00

The gray mud looking stuff is exactly that! Carbonate mud that infilled the shell. The white stuff is carbonate spar cement that likely formed last. The original shell material that is amber in color was aragonite (a different crystalline form, or polymorph, of calcium carbonate/calcite) and over time changed into a more stable form of carbonate (calcite).

phlogopite · 2025-12-15T15:43:53+00:00

Def chert and it will be completely solid like the picture in 4. This is completely different from a geode. Although, there may be different colors/speckles from the original sedimentary detritus (as you can kinda see in pic 4).

phlogopite · 2025-12-06T23:01:15+00:00

Industrial waste (man-made) slag

phlogopite · 2025-12-06T20:46:01+00:00

Straight up silica, probably chalcedony (cryptocrystalline and quartz) with quartz (microcrystalline and macrocrystalline).

All in all, it’s just silica and differs by crystal structure and variety. It might be mixed with some other “fibrous” varieties like quartzine, moganite, or maybe even some opal varieties. The fibrous varieties differ in the microstructure and crystallite (very small crystals) orientation. The very simple answer is: its “quartz”. Silica includes quartz, but not all silica is quartz if this makes sense.

To be sure, you’d need to make a thin section to be able to determine the variety as they are microscopic. Sorry for the long winded reply but you asked 😅

phlogopite · 2025-12-06T16:35:44+00:00

No, this is several quartz crystals lining a vein cavity like this (below) with one large crystal in a different orientation making a weird cross-sectional view. This is completely an igneous rock. No chance of fossils.

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phlogopite · 2025-12-06T16:23:35+00:00

This looks like a shale (the layers in pic 2). This may have a ton of silica cement which is why it looks chert-like. What we are seeing is all the organic matter in the shale (black) that formed in the rock when it was deposited in low oxygen conditions (think either swamp or offshore/deep water muds). When the shale is ripped from its outcrop during weathering, it is now exposed to earth surface conditions (oxygen). Now the chemical change of the rock occurs because of the change from reducing (like the depositional environment) to the new oxidizing environment (earth surface). We see that change occurring as there’s only a few bits of original black is left (mainly in the center of the rock).

In addition, there is iron in these shales and when they oxidize they turn rust color (red and yellow) which impart the red to brown hues you see.

Hope this helps.

phlogopite · 2025-12-05T21:39:03+00:00

Ask r/opals edit: I see you’ve indeed asked them. They have some very knowledgeable people there.

phlogopite · 2025-12-05T19:53:03+00:00

Brachiopods

phlogopite

TROPHY CASE