Small specimen which comprises a rib edge of parketted fluorite crystals with reddish iron oxide (eisenkiesel quartz) to the faces. When viewed with backlight the fluorite is grey green with some cleavage refraction within. From a classic German locality, the Erika mine (Wölsendorf fluorite mining district), Säulnhof, Stulln, Schwandorf District, Upper Palatinate, Bavaria, Germany, it measures 50x27x22 mm and weighs 46 g. Ex-Mineralien Museum Andreas Gabrys, Lam, Bavaria, Germany (see below).

Please note: this particular item is not large and is classed as a miniature-sized specimen (4.5-7 cm).

[The Mineralien Museum Andreas Gabrys was a privately run museum with a huge collection of more than 10,000 mineral, rock and fossil specimens. Located in Lam, Bavaria, Germany, the family owned museum was founded in 1969 by Andreas Gabrys, mine manager at the time for the Fürstenzeche (otherwise known as the Oswald mine) in Lam, and it had been open to the public until 2004. The small museum was run by Andreas and his wife, until he died in 1994. She then continued to run it for ten more years when, due to her age and illness, it became necessary for her to move into a nursing home. The museum was temporarily closed in the hope that someone in the community or a commercial enterprise might be found that would be interested in keeping things going, but sadly that was not the case. The son of Andreas, Manfred Gabrys together with his wife (both elderly themselves), became responsible for the museum and its large mineral collection. Although they wanted to keep the collection together and fully intact as a legacy to Andreas Gabrys, when a buyer could not be found for the museum and contents as a whole the building was put on the market and the collection was subsequently auctioned off in partial lots and dispersed.]

The Erika mine is located in the famous Wölsendorf fluorite mining district of Bavaria in south east Germany. Mining in Wölsendorf started in the 15th century or earlier. In the beginning, lead ore was mined. The extraction of fluorite started in the 19th and 20th centuries. The last mine was closed in 1987 (Hermine mine). It is not known when the Erika mine was first worked, but in a report written in May 1908 no mining activities were mentioned at that time. However, there was a dyke that was worked above ground for fluorspar. Between 1923 and 1930 the workings went by the name of Pit Lanzenleite. During this period, machines were set up to sink a hoisting shaft (eventually down to 39 metres) and a headframe was erected. However, in 1930 the owner ran into payment difficulties and subsequently filed for bankruptcy as a result of the poor sales situation brought about by the Great Depression and the whole property was auctioned off. It was bought in the same year and renamed Erika in 1931. Put back into operation, further developed and connected to the power grid, Erika mine was heavily worked for fluorspar between 1940 and 1945, along with the neighbouring Cäcilia mine, Johannesschacht mine, Marienschacht mine and Roland mine. However, in May 1945 all shafts and underground facilities of the Erika were flooded by bombing raids targeting the power grid. From August 1945, because of the coal crisis, miners worked the lignite that was found in parts of the mine. In 1948, fluorspar and baryte production/processing resumed at the Erika mine and it continued to produce for 21 years, being the most productive pit in the Wölsendorf district with a vein line of only 200 to 300 metres. In 1958 the Erika lignite mining operation was shut down. In their latter years, the main works of the Erika mine, Hermine mine and Cäcilia mine had all become interconnected underground because the main passages were connected. Together these three mines were responsible for more than half of the total production in the Wölsendorfer fluorspar district. In 1973 the Erika mine was shut down and in February 1974 the shaft was filled in. As of July 2009 at the former mine site, one building is used privately as a weekend home. The building with an office wing and a winding machine room including the adjoining nearby open spaces is used by a motorcycle club, even during the week, until late at night.

Fluorite (a halide) is considered to be one of most popular minerals in the world among gem and mineral collectors, second only to quartz. Fluorite is actually colourless although samples are often deeply coloured owing to impurities. It is often referred to as “the most colourful mineral in the world” owing to its variety of brilliant colours. Every colour of the rainbow in various shades are represented by fluorite samples, along with white, black, and clear crystals. The most common colours are purple, blue, green, yellow, or colourless. Less common are pink, red, white, brown, and black. Colour zoning or banding is commonly present. The colour of the fluorite is determined by factors including impurities, exposure to radiation, and the absence or voids of the colour centres. Translucent to transparent with a vitreous lustre it can appear as well-formed coarse sized crystals; also nodular, botryoidal, rarely columnar or fibrous; granular, massive. Fluorite was first described in 1530 and was originally referred to as fluorspar. In more modern times the mineral was recognised for its effectiveness as a flux for aluminium and steel processing. Today, the term ‘fluorspar’ is primarily used for the industrial and chemical form of fluorite, while ‘fluorite’ is the term used in reference to the gem and mineral. In 1852, the phenomenon of ‘fluorescence’ was named after fluorite, since it was one of the first fluorescent minerals studied. Mohs hardness 4.

Eisenkiesel is a translucent to almost opaque quartz that is coloured red, orange or brown by haematite inclusions. The term ‘eisenkiesel’ is sometimes also used in a wider sense, as a synonym of ferruginous quartz, for any quartz with iron oxides and hydroxide mineral inclusions (haematite, limonite) that is yellow, olive, orange or brown. The name is a German term, translating to iron quartz. ‘Kiesel’ was originally a term for quartz, but has changed meaning over time. In today's use, the word mostly refers to a pebble. On the other hand, silicic acid is still called ‘kieselsäure’ in german, because it is derived from quartz as its anhydride. Nowadays, people generally refer to eisenkiesel as quartz that is evenly coloured by inclusions of haematite. Hydrous iron oxides form and precipitate from watery solutions at relatively low temperatures, whereas haematite can also form in high temperature environments. Thus, ferruginous quartz can often be found in sedimentary rocks in and near hydrothermal veins and in the iron hat (the weathering zone near the surface that is altered by oxidising surface waters) of iron ore deposits.

Quartz (a tectosilicate) composed of silicon and oxygen (silicon dioxide), is the second most abundant mineral in Earth's continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, and since antiquity varieties of quartz have been the most commonly used minerals in the making of jewellery. The word quartz is derived from the German word ‘quarz’, which had the same form in the first half of the 14th century in Middle High German and in East Central German and which came from the Polish dialect term ‘kwardy’, which corresponds to the Czech term ‘tvrdý’ (hard). The Ancient Greeks referred to quartz as κρύσταλλος (‘krustallos’) derived from the Ancient Greek κρύος (‘kruos’) meaning icy cold, because some philosophers (including Theophrastus, successor to Aristotle in the Peripatetic school) apparently believed the mineral to be a form of supercooled ice. Today, the term rock crystal is sometimes used as an alternative name for the purest form of quartz. Mohs hardness 7.