The Mineral Quartz | Facts Varieties and Photos
Quartz | Type of Ice that Never Melts
Quartz is the most common mineral in earth's crust after ice and feldspar. It can be found in almost every geological environment and is a component of virtually every rock type.
It's the world's most diverse mineral in terms of varieties, colours and forms because of its abundance and widespread distribution.
Quartz can be found in sedimentary rocks as grains of sand and as crystals in igneous and metamorphic rocks. Quartzite which is composed almost completely of quartz is produced through the metamorphism of sandstone.
Silicon dioxide also known as silica is a chemical compound of two of the most abundant elements in Earth's crust, silicon and oxygen. It can be found most commonly in nature as the mineral quartz. It exists in several crystalline forms and a number of cryptocrystalline forms.
Quartz originates from the old German word 'quarz' first appeared in 1530. In ancient Greece it was known as 'krustallos' from 'kruos' meaning 'icy cold'. This is possibly because of the clarity of some quartz crystals.
Theophrastus the ancient Greek philosopher and successor to Aristotle believed colourless quartz was a unique type of ice that wouldn't melt.
Quartz cluster (Peru). Photo; Stan Celestian. Clickable image
The name rock crystal can be used to describe the purest varieties of quartz. In its purest form it's colourless and transparent.
Quartz occurs in two forms, crystalline which is usually abbreviated to crystal (quartz crystal) and cryptocrystalline which means crystals are too small to be seen with the naked eye.
Crystalline varieties can be colourless and transparent hence the term 'crystal clear'. They can also occur in many different colours from milky white to dark brown verging on black. Coloured varieties of tend to be translucent as opposed to transparent.
Stones with impurities are known as quartz with inclusions or included quartz.
The optical properties in quartz crystals led to its extensive use in lenses and prisms. It was once widely used in electronic components although has now been replaced with a synthetic alternative.
Quartz was the first crystal to be used in radio transmission and was essential in the development of computers. When mechanical pressure is applied to a crystal it returns an electrical charge.
Pure crystalline quartz with the mineral sodalite. Photo; Stone Mania. Clickable image
On Mohs scale of mineral hardness quartz grades 7 which is relatively hard. It's important to note that hardness refers to a stone's resistance to being scratched and is not the same as toughness. Tenacity which is the correct geological term describes a rock or mineral's resistance to being broken, crushed, bent or misshapen.
Despite being quite hard quartz is brittle so will break or shatter easily.
Different Quartz Varieties
Translucent variety of chalcedony known for its distinctive banding
Type of translucent quartz usually identified by its platy inclusions
Reddish to rich orange coloured quartz. Translucent variety of chalcedony. Sometimes referred to as cornelian
Variety of microcrystalline quartz, white in its purest form. Most types of chalcedony have their own unique name such as agate bloodstone or carnelian
Combination of colourless or milky white quartz combined with amethyst. Named for its chevron-like markings. Tends to be known as banded amethyst in the UK
Translucent apple green variety of chalcedony. The colour comes from nickel
Inclusions are common in quartz and although some varieties have their own name, most are known as included quartz. Tourmalinated and rutilated quartz are probably the best known varieties
Cryptocrystalline variety of chalcedony. Features fine inclusions of varying amounts of other minerals and substances. These cause the stone to be opaque and are responsible for its colour
White to greyish-white translucent to opaque variety. Often occurs in the same deposit as rock crystal
Striped variety of agate with alternating black and white bands. The name is widely used incorrectly
Pink coloured stone usually translucent. Crystal habit is massive. Pink quartz which is considered to be a different variety is often confused for rose quartz. The main difference is crystals are quite common whereas in rose quartz they have never been found
Colourless and transparent, its name came about during the late Middle Ages to differentiate it from a newly produced colourless material known as glass. At that time glass was known as crystal or crystal glass
Translucent to transparent mineral that occurs in various shades of brown. Colour can vary from light to so dark it almost appears to be black. Sometimes incorrectly referred to as smoky topaz which is a completely different mineral