[Rockhounds] Crystal Puzzle Much Closer to Solution

[R. Peter Richards]

One further thought.  If your specimen is feldspar, it should show  
two directions of cleavage at right angles (or very nearly so); one  
of these is perfect and the other less so.  None of the other  
minerals that have been mentioned as candidates has more than one  
direction of cleavage, except bertrandite, which has four, one  
perfect ({001}) and three good (({010} and {110}, the latter with two  
sets of planes at 45° to the former).  Sorry, I'm not going to try to  
explain the Miller indices!  I feel quite confident that this is not  
bertrandite.

Pete Richards


On Jul 13, 2009, at 1:37 PM, Carolyn Reynard wrote:

> Thank you Larry, Pete R. , Axel,  Earl & Pete M.,
>
> The one face of broken partial crystal in question  is 2 inches  
> long,  another  face is 1 7/8 inches wide.
>
> I have thought about all you have mentioned. I rechecked the  
> hardness with metal hardness points, but this time studying the  
> scratch under the microscope.  I certainly was wrong about the  
> 7.5..Clearly it is in the feldspar hardness range 6-6.5.  The  
> texture is finely perthitic without much doubt. I am very familiar  
> with the texture of apatite and I don't believe it is an apatite..  
> I have tried to measure the angle of the crystal with my antique  
> paper and plastic Penfield Contact Goniometer. The one angle I  
> believe I can determine is 44 degrees. Certainly not hexagonal.
>
> I have posted two scanned images on http://rockhounds.ning.com
> Please go my page; Carolyn C. Reynard.
>
> I do intend to photograph the crystal this afternoon and post the  
> images. They should be better.
>
> I believe I fell into the trap of quick ID.  I listened to several  
> who identified it as beryl, all along I thought it must be feldspar  
> with the texture and fluorescence. I doubted.
> Most likely that is why I was trying to put the two together in a  
> pseudomorph.
>
> I feel quite comfortable now that it  is a feldspar. What say all?
>
> Carolyn Reynard,
> amateur geologist
>
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___________________________________
R. Peter Richards
rpr at heidelberg.edu
Morphological crystallographer





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