Quartz Mineral

 

a line of four dark coloured terminated quartz points

 

About the Mineral Quartz


Quartz which is the most common mineral in the Earth's crust after ice and feldspar is found in almost every geological environment and is a component of almost every rock type on Earth. It 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.

Quartz is the most diverse mineral in terms of varieties, colours and forms because of its abundance and widespread distribution.  The name which originates from the old German word "quarz" first appeared in 1530.  In Ancient Greece the stone was known as "krustallos" from "kruos" meaning "icy cold" possibly because of the clarity of some crystals.  Theophrastus successor to the Ancient Greek philosopher Aristotle believed it to be a unique type of ice that would never melt.  The term rock crystal is sometimes used as an alternative name for stones which are exceptionally pure.

This common mineral occurs in two forms, crystalline which is usually abbreviated to crystal (quartz crystal) and cryptocrystalline which is stone that's made up of crystals so minute they can only be vaguely seen even under high magnification.  Although the crystalline varieties are often colourless and transparent hence the term 'crystal clear', they can also occur in many colours from milky white to dark brown verging on black, these varieties are mostly translucent.  Stones that feature crystallized impurities are known as included quartz.  The optical properties of rock crystal led to its extensive use in lenses and prisms and it was also used in electronic components although it has now been replaced with synthetic crystal.

Quartz was the first crystal to be used in radio transmission and reception and was essential in the development of computers. On Mohs scale of mineral hardness it grades 7.

 

 

Types of Quartz

 

Agate
Translucent variety of chalcedony that's best known for its distinctive banding

 

Amethyst
Purple variety whose colour is caused by the presence of iron and manganese

 

Aventurine
A type of translucent quartz which can usually be identified by the presence of platy inclusions

 

Bloodstone
Dark green chalcedony which often features red markings caused by inclusions of the mineral hematite

 

Carnelian
Reddish to rich orange coloured quartz that's a translucent variety of chalcedony.  Sometimes referred to as cornelian

 

Chalcedony
This type of quartz is microcrystalline and white in its purest form.  It does however frequently contain inclusions of other minerals which bring about a change in colour.  Most types of chalcedony have their own unique name such as agate, bloodstone or carnelian

 

Chrysoprase
Translucent apple green variety of chalcedony whose colour comes from the presence of nickel

 

Citrine
Yellow to yellowish brown coloured quartz that's relatively rare.  Much of the commercial grade citrine that's available to buy is heated amethyst

 

Included Quartz
Inclusions are very common in quartz and although some varieties do have their own name, most are known simply as included quartz.  Material that features inclusions of either rutile or tourmaline are probably the best known

 

Jasper
A cryptocrystalline type of chalcedony with fine inclusions of varying amounts of other minerals and materials which cause its opacity and colour

 

Onyx
Striped variety of agate with alternating black and white bands

 

Rose Quartz
A pink coloured stone that's usually translucent, it tends to occur in massive form and crystals are rare.  Pink Quartz which is a different type of quartz is often confused for Rose Quartz, the main difference is that crystals are quite common

 

Rock Crystal
Colourless and transparent, its name came about during the late Middle Ages in order to differentiate it from a newly produced colourless material known as glass.  At that time glass was known as crystal or crystal glass

 

Sard
Translucent light to dark brown coloured chalcedony.  Until the Middle Ages sard shared its name with carnelian.  Gemstones with bands of white sard and chalcedony are called sardonyx

 

Smoky Quartz
Translucent to transparent stone that occurs in various shades of brown from light to so dark that it almost appears to be black.  Sometimes incorrectly referred to as smoky topaz but topaz is a completely different mineral.

 

Tigers Eye
Type of quartz whose rich golden yellow colour is caused by the presence of iron.  Stones are well known for exhibiting an optical phenomenon known as chatoyance

 

Milky Quartz
White to grayish white translucent to almost opaque variety of silicon dioxide.  Often occurs in the same deposit as rock crystal

 

 

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Further Reading

Information and Links from Wikipedia
Facts and Photos on Geology.com