What mineral is this?

[OwenT]

Found these on Douglas Creek near Wenatchee WA, these crystals are really brittle and they're pretty soft too. The powder is white when it gets crushed and at first I thought calcite but calcite doesn't have that shape.

 

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[huntsman53]

I could be wrong but my guess would be decomposing orange Fluorite!


Frank

 

[Rockhunter1620]

Yes but calcite can or does form in several different shapes and can be that color. It does mainly or primarily form in sedimentary limestone.
I'm curious about what type of rock groundmass you have that pocket in. It can help if you identify your host rock also.

 

[OwenT]

The whole area is basalt but right down at the creek where we were it seemed like a cementation of big chunks of basalt and other sediments. The actual crystals had formed in a cavity in the chunk of basalt, but outside of that basalt was softer stuff. Another observation, we found the pocket just upstream of an old dam so it was probably under water for a while.

 

[Eu_citzen]

Try a drop of acid on it and if it bubbles and fizzles - calcite.

 

[OwenT]

No fizz with vinegar but it got super brittle.

 

[Eu_citzen]

Can a knife scratch it?

 

[BurntBear]

Appears to be Calcite to me. That is an amazing find regardless!! Wow.

 

[OwenT]

Thanks, I thought it was pretty amazing too, first time finding something like this. What makes it even more amazing is that this pocket was just laying open like this right next to the creek, amazing something like this was still intact being in a pretty popular area and all. Also a knife does scratch it. My buddy has all the crystals right now so I'm relying on him to make these observations. I'm going to get some tomorrow from him and see if a penny scratches it, see what else I can tell.

 

[DDancer]

My sound silly but try hitting a small piece of it with a torch to test for sulfur. I'm inclined to believe its calcite as well however being in basalt could point to sulfur as its soft and breaks up easily like calcite. Usually sulfur breaks up and degrades pretty quickly but hey its an idea. Another possibility is a zeolite however I've never found one like that~~
That is a pretty fascinating find however. Check around where you found it some more and you may find other pockets. I've a few area's I know of in AZ where the basalt has little pockets running thru it. I've pulled out small egg sized, very thin shelled, quasi geodes from the vugs in the basalt.

 

[OwenT]

No sulfur but it will scratch a penny.