246 GYPSUM FAMILY. continued to be used for this purpose Hntil the middle ages; for Albiniis informs us, that in his time, the win dows of the dome of Merseburg were of this mineral. The first greenhouses, those invented by Tiberius, were covered with selenite. According to Pliny, bee-hives were incased in selenite, in order that the bees might be seen at work. It is used for the finest kind of stucco, and the most delicate pastil-colours. When burnt, and per fectly dry, it is used for cleansing and polishing precious stones, work in gold and silver, and also pearls. It was formerly much used by Roman Catholics for frosting the images of the Virgin Mary: hence the names Glacies Maries or Frauen-glas given to it. It has also been named Lapis specularis, and Gypsum speculare and gla ciate, from its resemblance to glass or ice. Observations. The Gypsum of Montmartre, near Paris, differs from the kinds already described, in containing a consider able portion of carbonate of lime : hence La Methrie, in his lately published work, entitled Lecons tie Minerahgie, describes it as a particular species, under the name Mont' martrite. The following description is extracted from the Lemons de Mineralogie, t. ii. p. 390. Montmartrite. Chaux sulphatec calearifcre, Lucas $ Hauy. C-ypsum of Montmartre. Its colour is yellowish. It occurs massive, but never crystallised. It is soft. It effervesces witb nit?;c acid.
