Quartz is a remarkably interesting gemstone with an equally fascinating family tree. You’ve probably heard of its most famous varieties, such as Amethyst and Citrine. You may even have some of the lesser-known types, such as Prasiolite and Tiger's Eye, in your collections. But did you know that the Quartz family also incorporates a whole host of other gems such as Chalcedony, Onyx and Jasper? If not, read on for an exploration of how all these wonderfully colorful stones fit into just one gemstone family.
This article is intended as an informative overview rather than a technical deep dive, so we won’t get too overwhelming with the hard science behind the Quartz family here. It’s worth knowing that Quartz is the second most bountiful mineral found in Earth’s crust, though the vast majority of this material it is not gem-quality. The name is believed to have originated in Eastern European countries where the word ‘quarz’ was used to mean ‘hard’. Indeed, on the Mohs scale of mineral hardness, Quartz is measured as a 7 out of 10. Very few gemstones are higher than a 7 on the scale, those that are include Topaz, Emerald, Sapphire, Ruby and Diamond.
THE SCIENCE BIT
Broadly speaking, the Quartz family is split into two classifications, known as Macrocrystalline Quartz and Cryptocrystalline Quartz.
This is the classification that is most often known simply as Quartz. It includes the more transparent to translucent stones such as Amethyst, Citrine, Prasiolite, Smokey Quartz and Rose Quartz. These stones tend to form as large crystals, and if you’ve ever seen the Amethyst or Citrine geodes in our TV studio, you’ll know that the different crystals are easily big enough to see with the naked eye.
This is the classification that can sometimes also be known as Microcrystalline Quartz, or simply as Chalcedony. It includes the translucent to opaque stones such as Chalcedony itself, Carnelian, Onyx, Agate and Jasper. These stones form with such incredibly tiny crystals that they often can’t be seen even under significant magnification. Stones in this classification can be further divided into fibrous and grainy varieties. These names are taken from the appearance of very thin sections of each gemstone under a microscope.
The chemical formula for all Quartz is SiO2, which is silicon dioxide. The formation of Quartz begins as magma is forced from deep within the Earth, picking up different minerals as it rises. When the essential ingredients are present, including the necessary silicon and oxygen, these minerals begin to crystallize as the magma cools. This magma has quite often forced its way into small pockets within the ground, causing a geode to form. Geodes look like ordinary rocks on the outside but, crucially, are hollow on the inside. Over millions of years, additional minerals will seep into these hollows as the crystallization continues. This often leaves us with beautiful pure Quartz, but sometimes impurities can seep into the geodes during formation, and the resulting crystals then take on a beautiful hue. Most Quartz family members feature a trigonal crystal system, though hexagonal systems have also been observed, often when the crystallization has taken place at a much higher temperature. Raw crystals tend to be six-sided and terminate in a pyramid.
Below, we’ve broken down the two different classifications to show you many of the most popular Quartz types and their myriad colors.
There are of course many other varieties, including White Quartz, which is sometimes also known as Optic Quartz or Rock Crystal. This is Quartz in its purest form, with no imperfections to cause varying hues. When it is completely clear of inclusions too, it is quite stunning in its own right. There are also very visually distinctive varieties known as Strawberry Quartz and Aventurine.
Quartz crystals are piezoelectric, a natural phenomena that has had a significant effect on the electronics industry. In the spirit of keeping things simple, the piezoelectric properties of Quartz basically mean that it will create a very small electrical charge if it is squeezed. It will also carry an electrical charge across the crystal, from one side to another. When this is happening, one side of the crystal is positively aligned while the opposite side is negatively aligned, not unlike a battery. The electrical charge is created when the gem is squeezed because the atoms within are having to realign themselves to remain in balance with each other, briefly giving the stone its charge. While it is charged, Quartz will oscillate (meaning it vibrates) exactly 32,768 times a second. By counting these oscillations, we can use Quartz crystals as a very accurate way of timekeeping.
Every electronic device you own that features a clock most likely has a tiny Quartz crystal buried deep within it, from your phone to your TV, your watch to your games console. The small battery you change in your watch every few years is helping to keep the Quartz crystal oscillating. It’s not exactly a pair of beautiful Amethyst earrings embedded inside your device, and these days many of these crystals are made from synthetic Quartz. But we thought it was a fascinating application of gemology all the same.
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