CHAPTER I. 
HISTORY AND DISTRIBUTION OF GYPSUM DEPOSITS. 
Gypsum with the Ancients. 
THE sulphate of lime, or gypsum, has the chemical formula 
CasO,+2H,O. When the water is absent the mineral is called 
anhydrite, a form: rarely found in nature and which is of no 
economic importance. The derivation of the word gypsum 
is not known. The origin often given, from two Greek words, 
y7 = earth and ew = to concoct, is without much doubt errone- 
ous. ! : . 
The mineral has been used in various wavs from very remote 
time. Pliny records that the conservatories were glazed with 
transparent gypsum, called lapis specularis, for preserving fruit- 
trees in winter, and that beehives were thus rendered trans- 
parent so the curious could see them working. On account of 
the soft lustre given to the light as it passed through these 
transparent plates, these ancient people were reminded of the 
light from the moon, and so named this variety of gypsum selenite 
from ceAnvyn—the moon. Selenite was regarded by these people 
as the most delicate variety of alabaster and was used by the 
wealthy in their palaces for windows, receiving the name of 
Phengites. It is said to have possessed the peculiar and very 
convenient property of enabling a person within the house to 
see out, while those without could not see in. 
The walls of the old temple of Fortuna Seia were constructed 
of stone supposed to be compact gypsum and ‘‘the interior 
though without windows was rendered sufficiently ight by rays 
transmitted through its semi-pellucid walls.’’* At Florence, 
1. Rees’ Cyclopedia of Arts, Sciences, and Literature, 1814. 
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