Crystal/Fossil ID

[KimTexan]

A friend of mine found this recently in the area of Belton, Texas in the undivided early Cretaceous.

He sent me the pic and asked if I knew what kind of crystal it was. I didn’t know so I asked him if I could post it here for him.

I’m not so curious about the fossil clam as the type of crystal it is. 

If you need more pics it may take a while, because I think he is out of town for a while.

@ynot

It does not look like calcite really, but I suppose it could be. It just looks harder than that. I forgot to ask him to do a hardness scratch test. Let me know if you have any ideas.

 

Kim

 

[Tidgy's Dad]

Looks like quartz to me. 

Drop of acid should settle it.

If it doesn't fizz, it's quartz. 

probably. 

[ynot]

I think it looks like calcite crystals, but could be deformed quartz.

A hardness and vinegar test will tell which it is.

[goatinformationist]

The growth habit is not calcite so I go with quartz. Still, the vinegar test will settle things.

[erose]

Pretty sure they are not quartz. The environment just wouldn't be right. I was thinking possibly dolomite or aragonite. We need a mineral collector to chime in.

[Ludwigia]

Hard to tell just from pics. Please tell us how the tests turn out.

[KimTexan]

Like I said he is out of town. I don’t know him that well other than a common interest in rocks and fossils.

I’ll message him about the tests.

My guess is that it is a carbonate mineral like calcite or aragonite. It doesn’t look like calcite so I’m leaning towards aragonite.

I have a number of pieces of aragonite, but none look quite like this. Some have the acicular form on parts so I know it’s aragonite. 

I’ll update you if I get any info from him.