FMF - Friends of Minerals Forum, discussion and message board

[bugrock]

Hello,

This past summer I purchased a Baryte specimen from the National Iron Mine, Marquette Co, Michigan. Specimens with this botyoidal habit are mentioned very briefly in Michigan Mineralogy (2004) and there are specimens in the Seaman Museum.

It looks like a chunk of cave formation and there are a number of broken botryoids. The breaks however reveal that there are thin rectangular holes that run down the axis of the rounded knobs. The "underside" of the piece appears to show negative casts of thin xls and also groups of short Baryte blades. The rectangular tunnels through the piece suggest the botryoids formed around a thin bladed mineral that has since dissolved away. If this was a prior generation of Baryte the blades must have been incredibly thin for that mineral. Celestine and gypsum might have formed in such thin blades.

The specimen measures 11.5 cm X 8.0 cm at the base. The rectangular holes measure up to 2mm in width but most are thinner.

Curious if anyone can shed more light on this occurrence and the possible mechanism of formation for such material.

Just in case you think you are experiencing deja vu, these images have also been posted on min dat message board.

Thanks,

George Balogh

[Pete Richards]

Molds of this sort are often attributed to anhydrite. Earlier Baryte is possible, but then you have to explain how you got rid of it while not getting rid of the botryoidal Baryte. Does happen, but not often.

I don't know anything about the geology of this particular mine, but I'd put my (minimal) bet on anhydrite.