Quartz Rock Crystal

Handmade in Bolton BBC IPlayer – Fatimid crystal Quartz Rock Crystal Quartz is a mineral consisting of silicon and oxygen SiO2 – a glassy mineral sometimes known as Rock Crystal. If it is to be used for carvings it needs to be clear without any inclusions. When other elements are present it changes its name: with iron it either becomes purple amethyst or yellow citrine; with manganese it becomes pink rose quartz; the brown of smoky or Cairngorm quartz is due to natural radioactivity and if there are tiny cavities and bubbles filled with CO2 or water then the quartz becomes milky. The quartz found in veins is usually milky and sometimes contains gold. Quartz also comes in cryptocrystalline forms such as chalcedony, carnelian, jasper, agate, bloodstone and onyx. Quartz is the most abundant and widely distributed mineral found at Earth's surface. It is plentiful and minable deposits are found throughout the world. It forms at all temperatures. It is abundant in igneous, metamorphic and sedimentary rocks. It is highly 1 resistant to both mechanical and chemical weathering. This durability makes it the dominant mineral of mountaintops and the primary constituent of beach, river, and desert sand. It is one of the hardest minerals – only topaz, corundum and diamonds are harder. Because of this it has many uses, but we’re going to look at the carving of pure rock crystal. The name Rock crystal is from the Greek krystallos, meaning ice, because the Greeks thought it was ice frozen forever hard by an unnatural frost created by the gods. Rock crystal can be found in some form in any geological environment that allows the formation of quartz in general. Large, well-formed and transparent crystals are found in some pegmatites and hydrothermal veins formed during the tectonic processes of mountain building. For crystals to form they must have space to grow and conditions which are consistent for a very long stretch of time. Gold in quartz formed in a hydrothermal vein. Large pure crystals of quartz are gemstones which, once cut, hollowed out, and polished, can be turned into remarkable and luxurious objects. Before the Islamic conquests of the 2 seventh century, Sassanid Persia was known for its quartz creations but it was in Egypt, during the reign of the Fatimids (969–1171) that the shaping of rock crystal attained absolute perfection and became an industry. There has been some dispute as to where they sourced their quartz but research has found that it was probably Madagascar. The crystal found there has high purity and translucency, sometimes single crystals weighing as much as 300 kg. The al-Aziz piece in the Treasury of San Marco, The Aga Khan’s ancestors, the Fatimid Caliphs of Egypt, founded the city of Cairo in 969 and prized the qualities of the rock crystal which they carved into vessels of different forms. Of the very few rock crystal objects existing today (180 in total), only a few can be securely dated back to the Fatimid period. A front view of a Fatimid Rock Crystal Ewer, shown above, is regarded as the most valuable object in Islamic Art. The ewer was carved from a single piece of very pure, very thin crystal. It was said that rock crystal glasses would shatter on contact with poisoned liquids, or the liquid changed colour, which is perhaps why they were so popular with rulers. 3 This rock crystal ewer is at the Victoria and Albert Museum in London. It is one of a series that survives in collections across Europe. Great skill was required to hollow out the raw rock crystal without breaking it and to carve the delicate, and often very shallow decoration. The body of the ewer is very thin (less than two millimetres thick on the undecorated part), making it very clear and light. Human skulls and skull imagery were known to have featured in Aztec art and iconography in Mexico. They were worked by Aztec, Mixtec and even Maya lapidaries. The British Museum has a crystal skull acquired in 1897 from Tiffany and Co. which they believed to be an ancient Mexican skull. However, when the skull was studied recently it was found that the tool marks were made by machine and it was not hand carved. Rotary cutting wheels were not introduced to Mexico until after 1521 and the Spanish conquest. Other evidence points to the source of the crystal. The Aztec’s would have used Mexican rock crystal but the British Museum skull was found to be crystal from Madagascar imported by the French in the late eighteenth century. It is a fake ! Today the best rock crystal sources are Brazil, Switzerland, Hungary, India, Madagascar, United States, Japan and Switzerland. Large individual crystals of quartz have been found in Brazil, the largest weighing over 44 tons. Although colourless quartz is relatively common, large flawless specimens of rock crystal are not, which is why crystal balls these days are made of glass, not quartz. 4.

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