Fluorescent Minerals For Sale
How Does Quartz Form?
Quartz is primarily made up of two elemental components, silicon (Si) and Oxygen (O), both of which are in high abundance on our planet. This combination typically occurs when water that's high in silicon content (often gained through the breakdown of the surrounding rock) seeps through cracks in rocks and ends up exposed to oxygen within cavities. In this environment, the silicon atoms will bond to oxygen and begin building layers that over time result in cavities lined with thousands of crystals. These cavities most often occur by means of tectonic activity, hollow tubes formed by lava, dissolution (breakdown of rock resulting in cavities) or even as solidified bubbles of gas within the earth (geodes).
Quartz formation within a vug/cavity - Silicon-rich solutions will deposit themselves along the walls of the rock cavities. Long crystals, also known as spears, can form in these cavities when the solution drips more from one location of the rock than the other, explaining why vugs often form a wide variety of crystal sizes in close proximity. The crystals will continue to grow as long as they're provided with the environment necessary for formation. In some instances, a surplus of these minerals will result in a solid vein of quartz where individual crystals can no longer be identified by the naked eye.
Quartz formation within a geode - While there is yet to be a conclusion as to how geodes form, it's widely accepted that they form by means of solidification of gas bubbles (vesicles) within basaltic lava during igneous rock formation and in round cavities within sedimentary rock. The necessary minerals for quartz formation precipitate into these cavities, depositing crystals (most often in an even layer) along the inner wall of the geode.
Quartz Crystal Formations
The type of formation of a quartz crystal is most often dependent on the environment in which it grows. Based on the structure and potential inclusions within the crystal, a lot can be learned about the history of its formation.
Quartz with inclusions - Inclusions often occur when foreign particles find their way into the silicate-rich solution. This can occur by movement of surrounding rock or just an overall change in the flow solution. Once these particles have a moment to settle, in some cases they’ll settle on the quartz crystal. The quartz crystal continues to grow, provided the environment is still favorable, resulting in the foreign particles becoming enclosed by the overlying quartz formation. This can occur over long periods of time (in some cases, millions of years) and in waves, sometimes resulting in quartz that displays multiple layers of zoning (phantoms).
Another way inclusions can occur is when silicon-rich solutions enter a cavity that had prior crystal growths. Rutile and tourmaline are two common minerals that quartz can grow around without interruption of the formation process. This results in some beautiful quartz specimens known as rutilated quartz and tourmalated quartz.
Tessin Habit Quartz Versus Artichoke Quartz - Tessin Habit, also known as expanding quartz, is a formation of quartz where the crystals dramatically taper down towards its termination. The base of the crystal will be much wider than the termination. This quartz formation occurs in high temperature environments of which the flow solution is high in carbon dioxide. Artichoke Quartz, also known as Rocket Quartz, has an opposite growth pattern, where the base of the crystal will be smaller than the termination. Secondary growth crystals usually surround the center crystal, sprouting out from the center crystal’s faces.
Faden Quartz - A type of quartz formation that’s typically found in mountainous regions, with Quetta and Northern Pakistan being the most well known deposits of these beautiful specimens. These quartz formations occur between cracks in a host rock. The cracks in the rock expand with the crystals, causing ruptures within the crystal from pressure. This rupturing results in “healing” of the crystal in a process that leaves behind a string/thread-like appearance that runs through the crystal formation.
Cathedral Quartz - Occurs when a secondary crystal grows parallel to another quartz crystal formation, often leaving the cluster with a cathedral-like appearance. This crystal formation can be seen in many quartz specimens that come from Brazil, as well as some found in Switzerland, Madagascar and Africa. Cathedral Quartz can be found all over the world, however these locations are known for producing some of the largest, most sought after specimens on the market.
Cactus Quartz - Also commonly referred to as Spirit Quartz, this formation of quartz has an aggregation of smaller, secondary crystals that formed in a ring around the center crystal. These secondary quartz crystals are most often at a right angle to the crystal that they form from, which gives the quartz a cactus appearance. The Magaliesberg Mountains of South Africa are well renowned for producing spectacular cactus quartz var. amethyst crystal clusters.
Scepter Quartz - This occurs when a knob-like growth of quartz forms on an earlier crystal. This is believed to happen when there is a change to the environment, like change in temperature, composition or direction of solution flow. The earlier crystal ceases to grow, while a secondary crystal forms at the original crystal’s termination. Provided the solution necessary for quartz formation is still present, the secondary crystal will begin to form, most often in the same orientation as the underlying crystal. Many times, an influx of iron into the silicon-rich solution will be enough to cause this dramatic change in the quartz crystal’s formation, explaining why many scepter crystals are found as amethyst (variety of amethyst).
Inverse Scepter Quartz - A formation of quartz that’s the opposite of scepter quartz. Caused by a reduction of silicon saturation within the solution, the growth of the crystal is altered, slowed and in most cases stunted. This can leave the quartz with a funny appearance similar to that of steeple or a bent finger.
Interrupted Quartz Crystals - Occurs when prior mineral growths interrupt the formation of a quartz crystal. Sometimes the quartz can continue to form relatively normally thanks to the magnetic attraction of the atoms, like in specimens interrupted by very thin sheets of calcite. Though sometimes the calcite (or other interrupting mineral) is too much for the quartz to engulf without deformation, resulting in obstruction and/or alteration of growth that leaves the crystal with a unique appearance. There are many quartz specimens from Dalnegorsk, Russia that display very strange, deformed quartz crystals because of these interruptions.
”Diamond” Quartz - A type of quartz crystal that forms in sedimentary rock. Often these crystals are relatively small, display beautiful clarity, have smooth faces that have the appearance of being faceted, are double terminated and their “diamond” name is often preceded by the location from which they are found, i.e. Pakimer Diamond (from Pakistan), Herkimer Diamond (from Herkimer, New York), etc. It’s believed that these crystals form slowly and at a relatively low temperature, explaining their unique clarity and structure.
Varieties Of Quartz
Agate - Commonly associated with igneous and metamorphic rock, occurring within cracks and cavities. Forms in banding patterns from a flowing solution. Can be multicolored and most often displays some translucency.
Jasper - An opaque variety of cryptocrystalline quartz with conchoidal fracturing. While most often being red to yellow in color, it can also be green and blue dependent on chemicals present during formation. A jasper specimen is typically multicolored.
Chert - Very similar to jasper in that it's a cryptocrystalline variety of quartz, however the key characteristic that determines whether a specimen is jasper or chert is the color. A jasper specimen that is a dull brown with no color variation will often be classified as a chert.
Amethyst - A purple variety of quartz that owes its violet color to natural irradiation, iron impurities, and the presence of trace elements, which result in complex crystal lattice substitutions. It’s considered a semi-precious gemstone, and just two centuries ago was considered to have a value on par with diamonds, sapphires and rubies.
Citrine - A yellow to amber colored variety of quartz. The yellow color is a result of ferric impurities within the crystal lattice. Most natural citrine specimens are small and are considered to be quite rare. Most of the larger specimens on the market likely gained their color through unnatural processes, such as heating. If the price for a nice "citrine" specimen seems too good to be true, it likely is.
Prase - A leek-green variety of quartz, often gaining its color from inclusions like hedenbergite.
Prasiolite - Similar to prase quartz, this variety of quartz is also green, however it's quite rare. It is found bearing translucency and a mint-green color. It only comes from a handful of known locations around the world, meaning many specimens on the market are actually heat treated or radiation tortured amethyst.
Rose Quartz - A pink variety of quartz that is found in large masses, as opposed to being found as individual crystals. This pink color was thought to be attributed to impurities of titanium, iron and/or manganese, however an x-ray diffraction study in 1987 showed that it was due to inclusions of microscopic fibers which were thought to be the mineral dumortierite. Even more recent analysis using other techniques have shown the microscopic fibers are an unidentified or unnamed mineral that is closely related related to dumortierite.
Smoky Quartz - A grey-brown to black variety of quartz. This common name is derived from from the appearance of smoke within the quartz crystal. Dependent on the location and the chemicals present during formation, smoky quartz can appear opaque black, however it’s typically translucent to some extent. It’s believed that the quartz gains this color from a combination of natural irradiation and aluminum impurities.
Tiger's Eye - A variety of quartz that has a fascinating and constantly shifting light effect where the gold and brown bands appear to keep reversing as the stone is moved relative to the light source. It gains this chatoyant property from subparallel intergrowths of quartz crystals and altered amphibole fibers that have turned into limonite. It's primarily used for ornamental and lapidary purposes. Primary sources of Tiger's Eye are South Africa, Australia and China.