last modified: Tuesday, 26-May-2009 03:44:48 CEST
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Quartz occurs in very different forms and many of them have been given their own name, and are called a quartz variety.
There is no strict definition of the term "quartz variety". Varieties are distinguished by visual properties (color, transparency, etc.) and by being or not-being crystallized, although this is an over-simplification.
Some authors distinguish color varieties and form varieties that differ in their growth patterns and shapes. I only call color varieties "varieties"; form varieties are dealt with in the chapter Growth Forms, and I do not call them varieties, for the following reason: even a small, incomplete fraction or sample of a crystal can still be identified as a specific color variety[1], but this does not work for growth forms. A color variety does not loose any of its specific qualities when cut, but a form variety will. So when a jewel is cut from an amethyst scepter quartz all that will be left is an amethyst and the scepter quality will be gone. This is merely a practical consideration and if someone else decides to call a specific growth form a variety, I will not object to this.
The best example for a quartz variety is amethyst:
- it has a well defined color
- the cause of the color is identical in all specimen and is well understood
- it has a characteristic internal structure[2]
- the morphology of the crystals reflects the internal structure macroscopically
- these properties can be found in specimen at many locations all over the world
Other well defined quartz varieties are smoky quartz, rose quartz, pink quartz, and chrysoprase. Less well defined are blue quartz and plasma, for example.
So the naming scheme for quartz varieties is not "scientific", and you should not expect it to be fixed or consistent. It is a heritage from past generations that has developed slowly and has changed over time. In the Classical Times rocks were simply distinguished by their physical, namely visual appearence[3]. Many quartz varieties were considered a species of their own and of course given their own name. The following table presents those "venerable" quartz varieties. A "modern" list would be much longer.
| Name | Color | Diapheny | Habit |
|---|---|---|---|
| Agate | any color, banded |
translucent | dense |
| Amethyst | violet | transparent to translucent |
crystals, crystalline masses |
| Aventurine | green, red, brown, blueish |
slightly translucent, metallic shine |
dense, grainy masses |
| Carnelian | orange, red, brown | translucent | dense |
| Chalcedony | bluish gray, any color |
translucent | dense |
| Chrysoprase[4] | green | translucent | dense |
| Heliotrope, Bloodstone |
dark green with red spots |
almost opaque | dense |
| Jasper[4] | red, yellow, many colors |
almost opaque | dense |
| Onyx | black and white banded |
translucent to almost opaque |
dense masses |
| Prase | green | translucent to almost opaque |
crystals or dense masses |
| Rock Crystal Mountain Crystal |
colorless | at least partially transparent |
crystals |
| Sard | brown | translucent | dense |
Since the past 25 years or so, mineralogical societies have tried to come up with some canonical rules of how to name what (e.g. rose quartz and pink quartz are now officially two varieties)[5]. On the other hand, with the renaissance of esoteric culture a great number of new names have been introduced and add to the confusion.
Nevertheless it is possible to classify each quartz variety as belonging to one of two large groups: "macrocrystalline" and "cryptocrystalline" quartz.
Macrocrystalline vs. Cryptocrystalline,
or Quartz vs. Chalcedony
Those varieties of quartz that develop crystals were called macrocrystalline, as their crystalline structure is visible to the naked eye.
All others were labeled cryptocrystalline or microcrystalline, as their crystal structure was "cryptic".
Based on that criterion, we could list a few quartz varietes in a table like this:
| Crystals visible | Crystals invisible or absent |
|---|---|
| Amethyst | Agate |
| Eisenkiesel | Aventurine |
| Prase | Chalcedony |
| Rock Crystal | Flint |
| Jasper | |
| Rose Quartz | |
| Tiger Eye |
However, when you look it up in a good book, you will more likely find the same varieties sorted like this:
| Macrocrystalline | Cryptocrystalline |
|---|---|
| Amethyst | Agate |
| Aventurine | Chalcedony |
| Eisenkiesel | Flint |
| Prase | Jasper |
| Rock Crystal | |
| Rose Quartz | |
| Tiger's Eye |
Tiger's eye, aventurine[6] and rose quartz will be listed under macrocrystalline varieties. Why is rose quartz put into the group of macrocrystalline varieties, although crystals are completely absent?
Rose quartz has a homogeneous internal structure, a property it shares with the other members of the group, as opposed to the fine grainy or fibrous structure of cryptocrystalline varieties. This reasoning also holds for tiger's eye and aventurine, although it is not immediately clear what "homogenous structure" means in their case.
Cryptocrystalline varieties are so-called textural varieties of quartz, and more similar to rocks (like marble or quartzite), as they contain considerable amounts of other silica modifications and water.
The difference between crypto- and macrocrystalline quartz is more thoroughly discussed in the chapter Types of Quartz.
The Naming "Problem"
As I said, there is no clear, consistent and commonly accepted terminology or taxonomy of quartz varieties and growth forms. Especially when inclusions cause a specific color, the names seem to be chosen arbitrarily.In esoteric circles the shape of the crystal is said to reflect its powers. This has introduced a lot of new terms, although they are hardly ever used by collectors.
Then there are people like me, quartz collectors, who need to get every possible type of quartz, and traders react to that and make up their own labels for quartz varieties and growth forms (a strategy known as "market diversification" in economy). So suddenly there is "tangerine quartz" and "orange quartz" (no difference between them), "lemon quartz", "strawberry quartz", cathedral quartz, pagode quartz, elestial quartz, etc.
The number of names for agate "varieties" is probably greater than that of all other quartz varieties and growth forms put together. I will therefore only describe the most important forms and those names that are widely used.
So the "phonebook" of quartz varieties will be ever-growing and I cannot possibly cover all the different names on this page. Should you have problems finding a specific variety or growth form, first check the Table of Synonyms.
Footnotes
1 There is actually one exception form this "rule": ametrine can only be identified as such if the sample contains both amethyst and ferruginous parts, otherwise it will appear as an amethyst or ferruginous quartz/citrine.2 Almost all amethysts exhibit a specific kind of twinning. There are exceptions from this general rule, however.
3 At those times stones were widely used for healing, and in medieval medicine their specific healing power was often determined by resemblance with another object, e.g. an organ. In ignorance of their similar nature, quartz varieties have been attributed different powers.
4 In the Classical World the terms "chrysoprase" and "jasper" stood for some other, but unknown, precious stones and not the quartz varieties.
5 This process is not and will probably never be completed, as the whole matter is in a tension field between the traders who try to sell another fancy variant, the collectors who try to find a box for everything, and the scientists who only shake their heads over such a vigorous discussion about something so unimportant.
6 Aventurine is actually a mixture of macrocrystalline quartz and other minerals, and some books will accordingly not call it a quartz variety, but a rock, not unlike quartzite.
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