Dobby Diamonds

[chrisski]

I'm asking for some help in identifying this Crystal which the locals call a
dobby diamond. Definitely no expert here, but most puzzling to me is these
crystals have no transparency whatsoever and are not the slightest bit
shiny.

These crystals are found in the state of Montana and in the area they come
from there's quite a few of them. They are either found loose, or the host
material they come from is a redish white conglomerate where the
conglomerate material is small and rectangular. This conglomerate is rather
loose and can be cracked with a fingernail.

The crystal has no transparency, and looks the crystal shape is about a half
inch with 18 sides. It's a dodecahedral with six extra sides. The vertices
of the 12 of the 18 sides is triangular, and the other six sides are
rectangular. I've attached a sketch of the top view and side view. I've
seen a reference where this may be a partially tapered hexagonal bipyramidal
shape.

Also the crystal itself is a very soft material, I would guess a three on
the Moh's scale. The crystal can also be crushed really easy, and none of
the corners are sharp, all rounded.

My uneducated theory is this was formed in a shallow, superheated mud, for
long periods of time where certain minerals were leached out of the mud
forming the crystals, leaving the whitish red concretions left over. As the
host material erodes, its softer than the crystals, and that's why the
crystals can be formed over the area.

Edited July 22, 2015 by chrisski

[Idaho Jim]

Interesting. I've never seen one. I wonder what the specific gravity is?

Jim

[adam]

Looks like a mineral I used to have but cant remember the name. I do remember that it tasted like salt

[adam]

Now I remember. It was a mineral called Hanksite sp?

[clay]

Dang you are good Adam! Hanksite is a very good possibility - hexagonal, bipyramidal, soft and dark.

Now all we need is for Chris to lick it.

[chrisski]

I thank everyone for your help on this. I've got a trip for a couple of weeks and once I get back I'll take a specific gravity. I'd rather not lick the stone, I would say because it was loaned to me, but I'm not quite ready for that. The guy who loaned these to me is off to Montana and will try to find more. I've asked him to see if any locals know more about these.