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Ulexite vs. Satin Spar Selenite

Posted by zimmjm  
zimmjm
Ulexite vs. Satin Spar Selenite
October 24, 2003 06:04PM
How does one determine the difference between ulexite and satin spar selenite? They both seem to exhibit the same features (i.e. being transparent and bringing images underneath the rock to the surface). I realize that the two stones have a completely different chemical composition; ulexite being hydrous sodium calcium borate and selenite being hydrous calcium sulfate. However, I've seen both minerals described as "TV Rock" and I can't seem to tell the difference.

Thanks for your help.
Rob Woodside
Re: Ulexite vs. Satin Spar Selenite
October 26, 2003 08:56PM
Ulexite gives a better picture. Ulexite has a slightly greyish tinge and gypsum is often slightly tan or beige. Ulexite is a tad harder (2.5 vs 2) and gypsum a tad denser (2.1 gm/cc vs 1.9). Check out the fusibility, my memory fails me here but gypsm will decrepitate to a white powder and I think ulexite will fuse to a glassy bead?
Peter Haas
Re: Ulexite vs. Satin Spar Selenite
October 26, 2003 10:35PM
The following test should help:

Remove a bit of the material and grind it to a fine powder. Transfer the powder to a test tube and add some methanol (about twice the volume of the mineral powder), then add A FEW drops of concentrated sulfuric acid (pour it carefully down the wall of the tube). Mix well and heat over a flame. If the mixture boils, try to ignite the vapours escaping from the tube. If borate is present (ulexite), the vapours will burn with a green flame (volatile boric and boronic acid methyl esters). If sulfate (gypsum) is present, nothing happens.

There is no risk of a violent reaction - however, you must wear safety glasses. Also, since methanol is toxic upon inhalation, you must carry out the test in a ventilated room.

Regards
Peter
Peter Haas
Re: Ulexite vs. Satin Spar Selenite
October 26, 2003 10:38PM
The following test should help:

Remove a bit of the material and grind it to a fine powder. Transfer the powder to a test tube and add some methanol (about twice the volume of the mineral powder), then add A FEW drops of concentrated sulfuric acid (pour it carefully down the wall of the tube). Mix well and heat over a flame. If the mixture boils, try to ignite the vapours escaping from the tube. If borate is present (ulexite), the vapours will burn with a green flame (volatile boric and boronic acid methyl esters). If sulfate (gypsum) is present, nothing happens.

There is no risk of a violent reaction - however, you must wear safety glasses. Also, since methanol is toxic upon inhalation, you must carry out the test in a ventilated room.

Regards
Peter
Peter Haas
Re: Ulexite vs. Satin Spar Selenite
October 26, 2003 10:38PM
The following test should help:

Remove a bit of the material and grind it to a fine powder. Transfer the powder to a test tube and add some methanol (about twice the volume of the mineral powder), then add A FEW drops of concentrated sulfuric acid (pour it carefully down the wall of the tube). Mix well and heat over a flame. If the mixture boils, try to ignite the vapours escaping from the tube. If borate is present (ulexite), the vapours will burn with a green flame (volatile boric and boronic acid methyl esters). If sulfate (gypsum) is present, nothing happens.

There is no risk of a violent reaction - however, you must wear safety glasses. Also, since methanol is toxic upon inhalation, you must carry out the test in a ventilated room.

Regards
Peter
bill
Re: Ulexite vs. Satin Spar Selenite
October 27, 2003 02:18PM
ulexite -may be easy to tell by inferior hardness, lack of cleavage, not ordinarily in large crystals. Simple tests are not reliable since you can confuse results for the two minerals. Try and break a small chip and look at it with a loupe. You will see cleavage only in gypsum (selenite). Some satin spar will resemble ulexite. TV stone behavior will be similar for the two. Gypsum is harder but both are really soft compared to other minerals. Hope this will help. Bill
bill
Re: Ulexite vs. Satin Spar Selenite
October 27, 2003 02:21PM
ulexite -may be easy to tell by inferior hardness, lack of cleavage, not ordinarily in large crystals. Simple tests are not reliable since you can confuse results for the two minerals. Try and break a small chip and look at it with a loupe. You will see cleavage only in gypsum (selenite). Some satin spar will resemble ulexite. TV stone behavior will be similar for the two. Gypsum is harder but both are really soft compared to other minerals. Hope this will help. Bill
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