Despite the fact that it’s the 2nd most common mineral in the Earth’s continental crust, quartz is a true wonder of nature. Composed of the two most common elements in our planet’s crust (oxygen and silicon), quartz fascinated both scientists and common people since ancient times. At a molecular level, it forms extremely complicated (and variable) crystals, so going into more details there would require a considerable amount of detail – entire books have been written on that sole subject.
Quartz in itself is colorless and transparent (or translucent), but more often than not, it has some impurities. It’s these impurities that make it even more beautiful to look at. In this post, I’ll be ignoring the more practical uses of this amazing mineral and focus on aesthetics of its natural varieties (I’ll comeback with the practical uses in a post a few days from now, but just so you get an idea, quartz is absolutely crucial to the computer industry).
Perhaps the most striking representative of the quartz ‘family’, amethyst has been known and admired since the dawn of civilization – there are references to ancient Greeks and Romans that believed it prevented you from getting drunk and intoxicated (they even made drinking vessels of it). Also, if you placed one in the middle of your crop, it would protect it from pests and locusts.
There is still some debate surrounding its chemistry; it has the SiO2 composition (as every quartz variety), but the impurities that give it it’s violet color are still a topic of discussion. The most common possibilities are ferric iron and an interplay of iron and aluminum.
Color can range from a light pinkish to a deep purple, and there is quite a lot of it around, especially in Brazil, where the biggest mines are (it’s also relatively abundant in South Korea and Austria).
Most types of quartz have macroscopic crystals, but this is where chalcedony is different. It’s a cryptocrystalline form (crystals are barely visible even with a microscope) generally referred to as microcrystalline quartz in geology; because it alone has numerous varieties, gem dealers refer to each one by its name. If you plan on getting one, be careful however: numerous sellers just dye the rock, and for the inexperienced eye that can be hard to tell, because it can have a wide range of colors. Chalcedony also often psuedomorphs after organic materials, resulting in petrified wood (in Arizona, a whole forest has been petrified in this way), coral, etc. Types of chalcedony:
Citrine is the yellow variety of quartz (citrus means lemon in latin), and can be formed by two different mechanisms: the feric variety, with iron or iron oxide absorbs radiation (from ultraviolet to blue), and the second mechanism is still unclear, but it’s known that it’s caused by aluminum, lithium or hydrogen inclusions.
It’s easy to guess why the smoky quartz was given this name; the color ranges from brown to black, giving the vague impression that there’s smoke inside the mineral. It can be obtained either naturally or artificially. It also has two varieties, morion and cairngorm.
Rose quartz varies color from light pink to rose red, usually due to titanium or iron (but manganese can also be present). It’s rarely used as a gem, because in the vast majority of the cases, it has a lot of impurities, which is why it’s mostly used to carve animals, hearts, etc. However, when clear, it’s quite lovely.
So, there you have it – quartz can be quite different! You have to bear in mind that this is merely a visual separation of the types of quartz and I’ll ask you to excuse me for not using geological criteria that are more relevant; my goal was to show how unbelievably variate a single mineral can be, and raise interest for this matter. If I succeeded (or not) or you want to add something, please tell me.Click here for reuse options!
Copyright 2009 ZME Science
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