Quartz and Chalcedony Part 2
By Barry Taylor
There are so many classifications and varieties of Quartz that understanding this mineral can be a confusing and bewildering task. There is such a huge range of both colour and form that can be encountered, in part 1 the colours of Amethyst and Smokey Quartz were looked at. There are many other forms of coloured Quartz to be encountered, all of which have a slightly different reason for their shape and hue. To help with the identification the following is a synopsis of the most common varieties to be found.
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Ametrine as the name implies is actually a subtle mix of Purple Amethyst and Yellow Citrine, strongly coloured Amatrine can look stunning when polished and is in very high demand for jewellery. This type of quartz comes from a unique part of Bolivia, from one location called the Anahi Mine; recently other examples have been discovered in Brazil and India. This unique colour combination is actually due to variations in the main oxidising agent in the fluids of formation. Subtle differences in composition result in a mixture of the two Iron bearing forms Fe 2 and Fe 3, Ametrine has previously been given the name of Bolivianite or Trystine. Following high demand from the jewellery trade, a man made version has now been produced in Russia, this however has greenish yellow and Golden Blue as a bi-colour shade, both of these colours not found in nature.
An orange yellow to dark orange coloured variety, this often has visible inclusions of iron oxide, Citrine is also rarer than the Amethyst with which it is often associated, and Citrina is a Greek word for yellow. Some Citrine can be clearly found as a coating on top of milky quartz and I even own a small version that has in part a pinkish colour, all due to an infinitely variable mixture of the elements. The most abundant form of Citrine to be found is actually a man made version called Burnt Amethyst, this can be difficult to specifically identify but a sugary texture to the quartz base is characteristic, this is due to the effect of the heat needed to change the colour.
This is coloured by inclusions of very fine fibres of amphibole and has a very distinctive bright yellow colour. This yellow quartz is most often encountered in cut and polished versions from Brazil where it is also called Angel Quartz, this lovely yellow quartz is often also referred to specifically as Golden Angel Quartz by New Age followers. Another slight colour variation that can be found which also has a semi opaque orange hue and is called Tangerine Quartz, notably this occurs as long slender crystals as opposed the stubby crystals of Citrine itself. More recently a completely artificially enhanced version has been produced called Tangerine Aura or Dream Quartz, this material is produced by applying a very fine coating of Copper and Gold on to the surface of clear quartz, much like the other surface treatments using microscopic mineral coatings on clear quartz from the USA.
Rose and pink quartz
There are two distinct types of pink coloured Quartz, the most common variety is called Rose quartz and is actually only found in massive form, in pegmatite veins coloured by inclusions of Manganese or Dumortierite. Sometimes very finely scattered needles of Rutile in some examples produces the optical effect known as Asterism, this is best seen when cut as a cabochon for use in jewellery. The other variety that has clear pink crystals has a different crystal structure from the massive variety and should preferably be called Pink quartz. In addition to this are the small clear crystals found growing on top of a pink base of Rhodocrosite gives the appearance of being a pink quartz, this type originates from the old Inca silver mines of Peru.
Beautiful orange-red coloured crystals are well known from 2nd Sovietsky Mine, Daingorsk, Primorsky Kray, Eastern Russia.
All the natural red quartz has a colour that is influenced by haematite (iron oxide), mostly as a coating on top of clear quartz and this is also called Eisenkiesel from the German for iron pebble. One variety of this type of red quartz comes from the Florence Haematite mines, Egremont, Cumbria in the English Lake District; this produces a beautiful version where the dark red colour is actually just a thin coating on top of white quartz. Another subtype exists which has an Iron rich opaque dark red coating over Amethyst from the classic site of Thunder Bay, Ontario, Canada, another good location for this type of coating is in Hunan Province, China where there are iron mines. Superb doubly terminated crystals are also found in a Selenite matrix from Chella, Valencia, Spain and before that similar material came from Mexico, this is called Jacinto de Compostela. Finally there is a very obvious man made type from China, this is called Cherry Quartz.
This comes from a wide list of sources such as Kazakhstan, Brazil, Madagascar and Mexico and similar material that has brightly speckled phantoms of strawberry quartz included comes again from Hunan Province in China. In both cases the red fleck like inclusions are small flattened blades of Lepidocrosite exquisitely set in clear quartz, hence the indicative name of this variety. This type can be further subdivided on visual characteristics due to subtle variations in form applicable for each location from where these inclusions were first discovered. Red Quartz is also well known from the orange-red phantoms in clear white quartz from Orange River area, Namaqualand, Northern Cape Province, South Africa.
Harlequin Quartz also known as Fire Quartz, is similar to the above Strawberry Quartz but this time has stringers of black and red strands of Haematite and mainly comes from Madagascar, readers can find details in back issues of Rock n gem.
Super Seven Quartz
This is the name given to the spectacular material from Fundao, Espirito de Santos, Minas Gerais, Brazil; this displays a unique combination of material including Amethyst and Smokey Quartz. This is much sort after by new age followers. This mine was flooded in the 1970’s and is now closed and will produce no more material, therefore all that is available is old stock.
A lovely type of magical sky blue quartz is coloured by Iolite a variety of Cordierite or Shattuckite a rare hydrated copper silicate as micro-inclusions, most good quality material is snapped up by the jewellery trade. There are also other minerals that impart a blue colour to quartz such as Indicolite a blue Tourmaline from Minas Gerais, Itinga, Jenipapo District, Brazil. Often a clear micro-quartz can be found growing on top of blue minerals such as Chrysocolla, the covering of quartz looks blue due to the Copper minerals that impart colour in the overlying Quartz or Chalcedony. Kyanite is another blue mineral that can also
produce a similar appearance to any clear quartz associated with it. In the USA they produce a pseudo blue Artificial Quartz called Aqua Aura that is clear quartz covered with a microscopic coating of gold producing a strange blue that to my mind looks a little garish.
A clear light green variety is called Prasolite and this variety is produced by heating a Amethyst that comes specifically from the Montezuma deposit, Minas Gerais, Brazil.
Inclusions of Chlorite in clear quartz can frequently impart a green hue that is usually distinctly banded; other inclusions that impart a green colour are Prenite, Epidote, Actinolite and Aegrine. Avery dark green almost black Quartz is called Aventurine Quartz, this is coloured by Fuchsite and this has a sparkling appearance due to the included mica flakes, any natural green quartz is very rare and usually very pale in colour.
White or milky quartz
Often used by metaphysical followers (New Age Female quartz crystals). The colour here is due to millions of tiny air bubbles trapped in the quartz crystal as it grew. Witches fingers is a very poorly crystallised type of quartz of variable quality that has twisted crystal columns and multi growth features; this is sold almost exclusively to new age followers.
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