Log InRegister
Quick Links : The Mindat ManualThe Rock H. Currier Digital LibraryMindat Newsletter [Free Download]
Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsThe Rock H. Currier Digital LibraryGeologic Time
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
Search For:
Mineral Name:
Locality Name:
Keyword(s):
 
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsClubs & OrganizationsMineral Shows & EventsThe Mindat DirectoryDevice SettingsThe Mineral Quiz
Photo SearchPhoto GalleriesSearch by ColorNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryPhotography

Identity HelpUlexite vs. Satin Spar Selenite

24th Oct 2003 18:04 UTCzimmjm

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.

26th Oct 2003 20:56 UTCRob Woodside

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?

26th Oct 2003 22:35 UTCPeter Haas

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

26th Oct 2003 22:38 UTCPeter Haas

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

26th Oct 2003 22:38 UTCPeter Haas

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

27th Oct 2003 14:18 UTCbill

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

27th Oct 2003 14:21 UTCbill

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
 
Mineral and/or Locality  
Mindat Discussions Facebook Logo Instagram Logo Discord Logo
Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 23, 2024 15:39:16
Go to top of page