Selenite (mineral)
- Woman glass
- Mirror stone
- Selenite
- Lapis specularis
Marie Glass, Mrs. Glass, selenite or mirror stone, is a variety of the mineral gypsum and chemical point of view so that hydrous calcium sulfate ( CaSO4 · 2 H2O) of very high purity. The large, transparent crystals can very well split into thin flakes.
Etymology and history
The name selenite goes back to the Swedish chemist and mineralogist Johan Gottschalk Wallerius (1709-1785), who used it synonymously for transparent gypsum. The word derives from the Greek moon goddess Selene. It is believed that Wallerius was inspired by the pale - blue reflection of the mineral, similar to the moonlight to that name.
The common name in Germany Marie Glass was created through the use of a glass disc replacement before Marie images and relics in containers, because the thin leaves were free of bubbles and the same thickness as opposed to the former glass. By using the protection of Marie pictures, it is known in some regions as a woman glass.
The mineral was known to the Romans, who Lapis specularis ( mirror or stone - translucent stone - freely translated ) called. It was used by them for manufacture of windows. Although glass was at that time already known, but it was the quality, flatness and transparency not so good that from this window panes could be made . The Roman historian Pliny the Elder ( 23-79 AD ) described in his encyclopedia Naturalis historia the mining and processing of Lapis specularis to windows and lamps.
In Roman times, the most significant occurrences were in Asia Minor and North Africa. The at that time by far the largest deposit was located near the ancient city of Segóbriga (now Cuenca) in Spain. It is recorded that Pliny visited the local mines in the year 76. Remains of ancient mining activity can be found there today. Due to the rarity of larger selenite remained window panes made of this material prestige and luxury objects. It is known that some public baths in Rome had slices of selenite. Since the size of the crystals is limited, square cleavage fragments were assembled into larger discs, similar to today's bull's-eye. According to tradition, the emperor Tiberius had a greenhouse with discs of lapis specularis.
Education and Locations
Famous for their selenite crystal cave is in the Marienglashöhle to Friedrichroda in the Thuringian Forest. The largest naturally grown selenite in the world were discovered some time ago in the mine of Naica in Northern Mexico. The caves contain up to 14 m long and up to 50 -ton crystals of selenite.
Use
Finely ground mica is mixed as a historical pigment in coating materials, to give them a high brilliance. This effect is made to the Romans advantage by ausstreuten the floor of their amphitheater and hippodrome it. The ground Lapis specularis glared at the events when he was dusted.
Manipulations and imitations
Marie glass should not be confused with mica. This one can easily check: When heated it over a flame, turns selenite white and crumbles to powder. In older furnaces, the material for the window is often described as selenite. However, these are usually made of mica. In that selenite disintegrates in the heat, it is not suitable for this application.