Limonite Goethite? Any thoughts..

[Steve1236]

I found this cool little specimen while agate hunting, it's the only specimen like this I've found before out there, it has a brownish yellowish with a little rust red streak, hardness is between 6 and 7, steel knife wouldn't scratch it but sharp piece of quartz does if you press somewhat hard, specific gravity is 3.87, I'm thinking a little harder limonite goethite crystal maybe, could it be a psuedomorph? I'd love some second opinions...

 

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[Al D]

Looks like Staurolite

 

[Steve1236]

Thanks for replying and the second opinion alan m, it does resemble staurolite and has the same specific gravity but it leaves a streak so it's not hard enough to be staurolite, it would be cool if it were though.

 

[fuss]

Looks a lot like garnet.

 

[Steve1236]

Andradite did cross my mind but I thought not after doing a streak test, could it be limonite after andradite psuedomorph maybe?

 

[Steve1236]

Some more shots in sunlight...

 

[Buckshotnc]

Thinking some form of Limonite

 

[DDancer]

I'd go with Goethite, some forms of it have high hardness and the streak is right. Limonite and its variations doesn't get much harder than 5.5 so a knife will scratch it.

 

[Steve1236]

Yeah I believe it's probably a former mass of pyrite replaced by geothite, I guess it a common phenomenon.

 

[DDancer]

In some area's it is. Look up Devils Dice

 

[blauer]

Yeah I believe it's probably a former mass of pyrite replaced by geothite, I guess it a common phenomenon.

It's called a pseudomorph(ism), when one mineral is replaced by another but keeps the crystalized form of the former.

Here is an example (I have some of these specimens):

https://www.mcdougallminerals.com/product/goethite-ps-marcasite-14/

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https://www.mindat.org/photo-1033593.html