Marienglas
Marienglas , also known as women's glass , selenite or mirror stone , is a variety of the mineral gypsum and therefore, chemically speaking, water-containing calcium sulfate (CaSO 4 · 2 H 2 O) of particularly high purity. The large, transparent crystals can be easily split into thin leaves.
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 is derived from the Greek moon goddess Selene . It is believed that Wallerius was inspired to this name by the pale blue reflection of the mineral, similar to the moonlight.
The name Marienglas, which is common in Germany, arose from its use as a substitute for glass in front of images of the Virgin Mary and in reliquary containers , because the thin leaves, in contrast to the glass of that time, were bubble-free and uniformly thick. Because it is used to protect images of Mary, it is also called women's glass in some regions .
The mineral was already known to the Romans, who called it Lapis specularis (mirror stone or - loosely translated - transparent stone). It was used by them to make windows. Glass was already known at that time , but the quality, evenness and transparency were not so good that window panes could be made from it. The Roman historian Pliny the Elder (23–79) described in his encyclopedia Naturalis historia the mining and processing of lapis specularis into window panes and lamps.
In Roman times, the most important deposits were in Asia Minor and North Africa . By far the largest deposit at that time was located near the ancient city of Segóbriga (now Cuenca ) in Spain. It is said that Pliny visited the mines there in 76. Remains of the ancient mining activity can be found there to this day. Due to the rarity of larger selenite crystals, window panes made from this material have remained objects of prestige and luxury. It is known that some public baths in Rome had selenite disks. Since the size of the crystals is limited, square split pieces were put together to form larger disks, similar to today's slug disks . According to tradition, Emperor Tiberius owned a greenhouse with panes made of lapis specularis.
Education and Locations
The crystal grotto in the Marienglashöhle near Friedrichroda in the Thuringian Forest is famous for its Marienglas . The world's largest naturally grown crystals were discovered some time ago in the Naica mine in northern Mexico. The caves contain crystals of selenite up to 14 m long and weighing up to 50 tons.
use
As a historical pigment , finely ground Marienglas is also mixed into coating materials to give them a high level of brilliance. The Romans took advantage of this effect by spreading it over the floor of their amphitheaters and hippodromes . The ground lapis specularis sparkled at the events when it was dusted up.
Manipulations and imitations
Marienglas must not be confused with mica . This is easy to check: if you heat it over a flame, the Marienglas turns white and disintegrates into powder. In old ovens, the material for the viewing windows is often described as Marienglas. However, these are usually made of mica. Since selenite decomposes in the heat, it is not suitable for this application.
See also
Individual evidence
- ↑ General German real encyclopedia for the educated classes . 8th edition. tape 4 . F to Gz. FA Brockhaus, Leipzig 1834, p. 729 ( limited preview in Google Book Search - Glass window section ).
- ^ Great Names in History. Old Roman Specularis Mines. In: 100falcons.wordpress.com. February 10, 2014, accessed August 12, 2018 .
- ^ The crystal cave: searching for the Naica treasure. In: planetmountain.com. Planet Mountain, May 30, 2006; accessed August 12, 2018 .
- ^ The Giant Crystal Project Site. Gypsum - Gips - Plâtre - Yeso ( Memento from May 7, 2017 in the Internet Archive )
- ^ Crystal Cave of Giants. Naica, Mexico - Sept. 2009. In: stormchaser.ca. George Kourounis, March 26, 2013, accessed August 12, 2018 .
