Quartz exists in a whole variety of different, fascinating, forms.
Quartz also has fascinating properties that have been used for many, many things in modern and ancient civilisations.
Not least Piezoelectricity (and I am not quite sure how that should be pronounced! ) which is a feature of Quartz that creates electricity when mechanical stress is placed upon it. One if its first uses was in gramophone needles (where the vibration of the needle over the textured groove created a varying electrical signal). Later the reverse effect (whereby passing electricity through the crystal creates a regular vibration) was, and still is, used in clocks and watches … magical or what?
There are two main distinctions amongst the different quartz crystal structures: macrocrystalline which are crystals that are visible to the naked eye; and, microcrystalline, or cryptocrystalline, which are only visible under high magnification (such as in Chalcedony).
These differences in structure lead to the different properties. For instance Chalcedony is more soluble than quartz despite having an identical chemical identity and it is thought that this is because that as it is very finely grained (cryptocrystalline) and as result has a high surface area to volume ratio. Another example is Carnelian where people living in Central Asia used it to carve intaglios and rings bezels and seals because hot wax would not adhere to its surface.
There is so much one could write about all the different varieties of Quartz but there just isn’t space in a blog, so here is a brief synopsis of the major varieties.
Agate
Multi-coloured banded form of Chalcedony semi-translucent to translucent.
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Onyx
Agate where the bands tend to be straight, parallel and consistent in size.
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Tigers Eye
Gold-brown quartz which exhibits chatoyancy which is a changing of colour according to light like a cat’s eye.
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Rock crystal
Clear and colourless.
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Amethyst
Purple to lilac and translucent
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Citrine
Yellow to reddish brown or greenish-yellow.
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Rose Quartz
Pink
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Rose Quartz can also exhibit diasterism which is the phenomenon that creates a star effect as a result of light passing through it (as opposed to epiasterism which produces a star effect by reflecting light for example a Star Ruby cut as a cabochon).
Smokey Quartz
Brown to grey translucent.
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Carnelian
Reddish- brown Chalcedony
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Charlotte
© Copyright Charlotte M Bailey 2013
