[Rockhounds] Micro zeolite associates from Centreville, VA

[Kreigh Tomaszewski]

Mindat lists one source in Centerville

Quarry (MRDS - 10154716),  Centerville,  Augusta Co.,  Virginia,  USA

and notes it is a past producer. Epidote and Prehnite were the only 
minerals listed. Both minerals are relatively safe from most common 
cleaners, so pick a less valuable specimen and throw some chemicals at 
it.

Kreigh


On Friday, Jul 18, 2008, at 21:28 America/Detroit, R. Peter Richards 
wrote:

> In material said to be from the Virginia Crushed Stone Co., 
> Centerville, VA, I have vugs lined with prehnite.  Late stage 
> crystallization has produced loose stacks of microcrystals, or in some 
> cases, crystals impaled on byssolite fibers.  These crystals show 
> nearly all of their faces, making them a delight for someone like me 
> who likes crystal form first and foremost.  They seem to be of two 
> sorts, though both are platy with a six-sided morphology that is 
> consistent with orthorhombic symmetry.  One can think of a diamond 
> with the blunt angles cut off symmetrically.  (Man, it's hard doing 
> this without graphics!!!!)
>
> On one type, the truncating faces are shorter than the faces of the 
> basic diamond, the un-truncated points of the diamond are formed by 
> faces that meet at a bit less than 90° (from a photo I measure 82°), 
> and the faces are striated parallel to lines running between these 
> untruncated points.  If you're trained, think tabular on {001}, 
> bounded by {110} truncated by {100} or {010}.
>
> On the other type, the crystals are thinner tabular, the truncating 
> edges are longer, there are no striations, and the angles at the 
> un-truncated points are more nearly 120° (I measure 100°).
>
> Can anybody say if these are both the same mineral?  Are they both 
> prehnite (my guess)?  Does anybody have any additional information 
> about these beautiful microcrystals and their presumed mode of 
> formation?
>
> And can anybody offer any advice about how to remove the brown gunk - 
> smectite or something similar - without ruining these crystals?
>
> I can send digital images to anyone who is interested - contact me 
> offline.
>
> Thanks,
> Pete Richards
> -- 
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