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Re: hemihydrate (was: extinction6)

What is intriguing about anhydrite being present at "the boundary layer" is:
Anhydrite is an evaporite sedimentary roc - and it is not the first in the series to occur, halite, sylvite etc. will occur first; Too it can be a chemical precipitate as well. Evaporite materials will accumulate on the bottom directly beneath zones where corresponding densities (brine densities) exist in the surface waters. See Freidman, Sanders and Kopaska-Merkel, "Principles of Sedimentary Deposits" for more information on the behavior of chemical precipitates & evaporites in sedimentary deposits.

DB


At 6:11 PM -0500 2/14/04, Tetanurae@aol.com wrote: 
jedimr_thomas@hotmail.com wrote:
<<I guess not, 'cause anhydrite is greek for "without water", and my
Mineralogy-syllabus sais:
Gipsum: CaSO4.2H2O
Hemihydrate: CaSO4.1/2H2O
Anhydrite: CaSO4
of course this might be wrong nobody's perfect, but it seems logical>>

According to the Webmineral website, the mineral your professor is refering
to is known as Bassanite, 2(CaSO4)·(H2O), which essentially the same formula
listed by your instructor:

http://www.webmineral.com/data/Bassanite.shtml

There is no entry for Hemihydrate or anything close to that in its spelling.

Pete Buchholz
tetanurae@aol.com