Buz Groshong - Jul 13, 2012 1:01 pm - Voted 10/10
gypsumThey're actually gypsum or possibly barite that has crystallized in sand - often called "desert roses."
Scott - Jul 20, 2012 1:18 pm - Hasn't voted
Re: gypsumThanks.
I don't think it's gypsum since the "roses" are actually much harder than surrounding sandstone and gypsum tends to be soft.
I'm not sure about barite.
They're still made of a type of sandstone, but they are very hard and much harder than the surrounding rock.
Buz Groshong - Aug 4, 2012 12:00 pm - Voted 10/10
BariteI'd bet on barite. I have a specimen very similar to rhose in the photo that I have been told is barite. I suppose I could test it for specific gravity, which could prove that it is barite, but that seems like too much trouble. You shuld note that the sand in your picture is colored by iron oxide, but the blades of the "roses" are white, which is characteristic of barite. I've seen ones made of gypsum, but they are usually smaller and the blades on them are usually much thinner (less than 1 mm).
When you say that they are harder, I take it that you mean fracture hardness rather than scratch hardness - that just means that the surrounding rock is not very well indurated, which would be typical of a ferruginous sandstone.
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