Quartz crystals

Interesting facts about quartz


Pure quartz is completely transparent and colourless and, when it develops well-formed crystals, is called rock crystal. Quartz crystals are usually milky cloudy due to microscopic inclusions of liquids and gases (milk quartz) and appear grey when grown in the rock. Transparent to milky cloudy rolled pieces of rock crystal are also known under the name Rheinkiesel (Rhine silica), which originate mainly from the Alpine region and are found in Rhine gravel.
Varieties of quartz:


The violet colour of amethyst ranges from a very light, slightly pinkish to a very dark violet.

The distribution of colour in the crystal is usually irregular. More intensely coloured are usually crystal sectors that lie parallel to the main rhombohedron.
Amethyst is a widespread mineral; large and clear specimens suitable for processing as a gemstone are limited to comparatively few localities. Occurrences are found in Brazil, Uruguay, Namibia, Madagascar, Russia, Sri Lanka and Morocco. Such crystals are mainly found in cavities in hydrothermal veins and in volcanic rocks. So-called amethyst druses, where the crystals have formed within a cavity surrounded by a layer of chalcedony, are also frequently found in the trade. The most beautiful druses usually come from Brazil and can be as tall as a man.


Citrine is the yellow coloured variety of quartz. The name is derived from the Latin 'citrus' for lemon and refers to the lemon-yellow colour of this quartz variety. Depending on the origin of the citrine and the cause of the colouration, the shade varies from pale green-yellow to orange and brown-orange.
Natural citrine deposits are found in Argentina, Burma, Brazil (Maraba, Minas Gerais, Goiás, Rio Grande do Sul), France (Dauphine), Madagascar, Russia (Ural), Spain (Salamanca, Cordoba), USA, among others.
Citrine zones in amethysts are known, for example, from India (Hyderabad) or Brazil (Minas Gerais) as well as in citrine sectors in amethysts in Bolivia (Amahi mine). Natural, fired amethysts are known from a few localities worldwide.



Agate is a microcrystalline variety of the mineral quartz. What is striking about agate is its beautiful, striped pattern due to its rhythmic crystallisation.

Agate was held in high esteem from the earliest times. In Ancient Egypt, seal cylinders, rings, gems and vessels were made of agate around 1000 BC. In the Bible in the 2nd Book of Moses, 28, 17-20, the breastplate of the high priest, a plate set with precious stones, is described in detail. Amulets made of agate were supposed to help against lightning, storms and thirst.



Onyx is an opaque to faintly translucent, two-tone black and white, fibrous variety of chalcedony, which in turn is a variety of the mineral quartz. Agate is a similar, but multi-coloured variety.
Locations where onyx and sardonyx are found include Yemen, Brazil, Madagascar, Mexico, Pakistan, Uruguay and the USA.