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Quartz is a hard and crystalline mineral that consists of two oxygen and one silicone atom. It takes years to form this mineral under intense pressure. Quartz is the 2nd most abundant mineral found in Earth’s crust and is also considered to be the crystalline form of silicon dioxide. However, the process that forms quartz crystals is highly complex and requires immense pressure to form these crystals over the course of years.
Quartz Crystals typically grow in silica-rich molten rock, watery solutions of silica, and pegmatites with the help of the hydrothermal process. Hydro means “water,” and thermal means “heat.” This means that quartz crystals are formed due to high pressures in the presence of charged water solutions. The temperatures usually range between 100°C and 450°C, and the pressures are intense and high.
Today, you will learn the different geological environments of quartz crystals, and how these are formed in those locations. Moreover, you will also learn the chemical formulae that go behind creating these crystals. You will also learn the conditions necessary for the formation of quartz crystals at high pressures.
- How Quartz Crystals Are Formed?
- What Are the Physical Properties of Quartz Crystals?
- What Is the Bottom Line Here?
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How Quartz Crystals Are Formed?
The term “quartz” comes from a German word, “Quarz,” which means “hard.” On the other hand, the Ancient Greeks called quartz “krustallos.”
This term was derived from the Ancient Greek word “kruos,” which means “icy cold.” Together, these words became Quartz Crystal in the English language. The chemical formula for quartz crystal is SiO2.
Quartz Crystals are formed via the hydrothermal process and can be found in three different geological formations. These environments are:
- Silica-rich molten rock when it is cooling down and solidifying
- Pegmatites during the pneumatolytic processes
- Watery solutions of silica under high temperatures and pressures
In general, these quartz crystals utilize the hydrothermal process to add molecules to their surface and grow layer by layer. Let’s take a look at how quartz crystals are formed in all three different environments.
How Do Quartz Crystals Form in Igneous Rocks?
Macrocrystalline Quartz is among the most important elements for the formation of igneous rocks, such as silica-rich molten rocks or pegmatites.
These quartzes are either present before the rocks are formed, or are developed along with other minerals when the rocks are being formed. These quartzes later turn into quartz crystals via the hydrothermal process due to:
- An Abundance of Silica
- High Temperatures
- Intense Pressures
Igneous rocks, such as molten rocks, are a mixture of positively charged metal cations:
- Potassium, K+
- Calcium Ca2+
Moreover, these rocks also contain negatively charged anions, such as:
- Phosphate ion PO43-
- Silicate ion SiO44-
However, there are no SiO2 molecules in igneous rocks that serve as the founding elements for quartz crystal.
If you have ever seen lava before it is turned into molten rock, you must have wondered about the reason behind its viscosity.
This viscosity is a direct result of flexible molecules that tend to swim through the lava. Another reason behind this viscosity is the high amount of silica present in the rock itself. This silica turns the lava more viscous, and also plays a vital role in the formation of quartz crystals.
These flexible molecules are negatively charged. Moreover, these also contain hydrogen atoms in hydroxyl groups (-OH) in abundance. However, the relation of [O-] to [OH] relies heavily on the amount of water in the lava itself.
Since the molten magma cools quickly, typically while the volcanic eruption is happening, the period becomes too limited for the bonds in the SiO4-chains to split apart and form ordered structures of crystallized silicates.
When this lava cools down, it turns into volcanic glass. Therefore, it can be understood that a high level of viscosity plays a negative role in the formation of crystals and serves as an obstacle in this formation.
On the other hand, a low level of viscosity allows the bonds to quickly split and form new bonds of structured, ordered crystals, therefore, enhancing the overall process of crystal formation.
This also goes to show that silica-rich lavas have a higher chance of forming quartz crystals.
If the lava bursts and comes outside the Earth’s crust, it will cool down quickly. On the other hand, if the magma stays inside the Earth’s crust, it will cool down slowly, therefore, allowing quartz crystals to be formed.
The magma inside the crust will start to cool down eventually and start forming minerals and crystals of different chemical compositions depending upon the nature of the magma and its attributes.
Quartz crystals are the last to be formed inside a molten rock or an igneous rock. Therefore, these crystals basically fill out the voids and pockets of air that were left untouched during the formation of other minerals, such as:
- Mica Crystals
- Cryptocrystalline Quartz
This order of formation also determines some of the most important elements of quartz crystal, such as:
- Overall dimensions
Additionally, quartz crystals formed inside igneous rocks also offer an onion shape, meaning these crystals come with layers and layers of molecules hardened into crystals.
These outer layers take time to form, and you can see a significant difference in the color of different interior and exterior layers of a quartz crystal found inside a rock.
How Do Quartz Crystals Form in Watery Solutions?
Hot watery solutions, also known as hydrothermal environments, are a hotbed for quartz crystals in their purest forms. The hydrothermal process takes place at temperatures between 100°C and 450°C and requires high pressures to form the quartz crystals fully.
[SinOm]-OH + H4SiO4 → [Sin+1Om+2]-OH + 2 H2O
If you ever want to create orthosilicic acid, you can simply reverse this reaction and turn quartz crystals into this acid:
SiO2 + 2 H2O → H4SiO4
First, the individual orthosilicic acid molecules are dissolved into a hot water solution to increase the amount of silica in this solution.
These molecules quickly increase the amount of silica and create a hospitable and appropriate environment for the formation of quartz crystals.
These molecules either come from the nearby rocks, or from a scientist for an experiment. These hot water solutions are also quite rich in terms of ions and carbon dioxide. If the temperature or pressure drops, silica solubility decreases, so that the quartz solution is saturated.
Once the H4SiO4 compounds are applied to quartz grains in neighboring minerals, the crystals form a solution. If quartz grains are empty in the adjacent rocks, the H4SiO4 molecules add to form small floating crystals that bind H4SiO4 molecules more and more.
Only in a sufficiently oversaturated solution is this random forming of crystals feasible. The SiO4 tetrahedra is fully integrated into the quartz crystal.
On the other hand, if the temperature and pressure changes are constant and slow, there will no longer be small crystals.
However, the existing crystals will continue to grow, and SiO4 tetrahedra will be added one layer at a time to enhance further and complete these existing crystals.
Steady temperature ensures crystal formation, whereas, rapid changes in temperature essentially form smaller crystals and do not allow a full-fledged formation of crystals.
The formation of new crystals is not a pre-defined feature, but it depends on the temperature changes. Slow growth and constant temperature changes result in the formation of larger crystals. Fast growth and rapid changes result in the formation of odd-shaped smaller crystals.
The reason is that growth isn’t just because molecules are added to crystals constantly, it is the net result of molecular addition as well as removal.
Therefore, constant changes in temperature and pressure play a vital role in the overall formation of quartz crystals.
Moreover, during the formation of crystals, the molecules tend to chip away from the edges due to weaker bonding. This is why smaller crystals often get dissolved again during the hydrothermal process.
When the temperatures fall, the following things decrease as well:
- The solubility of silica
- The mobility of the H4SiO4
- The supply of new molecules
- The growth of the crystals will stop
Moreover, if there are hot brines in the equation, these will cause the entirety or rock to cool very quickly. This external element will result in the formation of the white vein or gangue quartz.
On the other hand, depending on the size of the lava body and the presence of hot watery solution in the cracks, the cooling process may take up to thousands of years.
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- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
What Are the Physical Properties of Quartz Crystals?
Quartz crystals are highly resistant to powerful chemical and mechanical weathering and are highly durable in nature.
This is why these crystals are most commonly found on mountaintops, beaches, and desert sand. Let’s take a look at some of the properties of Quartz.
|Color||Colorless, white, purple, pink, brown, and black, gray, green, orange, yellow, blue, and red, multi-colored or banded|
|Transparency||Transparent to opaque|
|Specific Gravity||2.6 – 2.7|
|Luster||Vitreous. Transparent, colorless Quartz crystals from a few distinct localities may be adamantine.|
|Cleavage||Indiscernible. Seldom exhibits parting.|
|Other ID Marks||Some specimens fluoresce, especially white and green.Triboluminescent.Piezoelectric.|
|Complex Tests||Dissolves in hydrofluoric acid|
|In Group||Silicates; Tectosilicates; Silica Group|
|Striking Features||Hardness, crystal forms, striations on crystal faces, and the frequent appearance of conchoidal fractures on crystal faces.|
|Environment||Quartz occurs in almost every single mineral environment.|
|Rock Type||Igneous, Sedimentary, Metamorphic|
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What Are the Different Uses of Quartz?
Quartz crystals are among the most abundant minerals found in the crust of our planet, and therefore, these crystals are used in a variety of things. Their physical and chemical properties make them suitable for a wide array of uses.
Quartz Crystals have a hardness level of 7 Mohs, and this makes them perfect for a modern era production process. Let’s take a look at some of the uses of quartz crystals.
How Are Quartz Crystals Used in Glass Making?
In the majority of modern geological processes, the extracted sand is almost made entirely of 100% quartz grains. These sand deposits are also known as one of the highest purity silica sand deposits.
Therefore, these sand deposits are used primarily for glassmaking. Quartz sand is used in the production of:
- Container glass
- Flat plate glass
- Specialty glass
Firstly, these sand deposits are melted into a liquid at high temperatures and pressures of 1700°C (3090°F). Once the sand deposit is melted, it doesn’t revert back to its original state upon cooling down. However, it does transform into an entirely different semi-liquid state with a new structure.
This semi-liquid state never turns into a completely solid state no matter how much it cools down. This frozen liquid state is also known as an amorphous solid, and it is also considered a cross between a solid and liquid with a crystalline structure that is later converted into the form of glass. This amorphous solid is then mixed with:
- Waste glass collected from recycling
- Soda ash (sodium carbonate)
- Limestone (calcium carbonate)
This combination of amorphous solid and other elements is then heated in a furnace up to a temperature of 1700 F.
The soda ash helps reduce the overall melting point of this sand deposit, and it also helps the manufacturer save energy costs and utility costs during the process.
If you only include soda ash into this mixture, it will produce glass that can easily be dissolved in any liquid or water. In order to prevent this drawback, limestone (calcium carbonate) is added that offers enough robustness to the glass so that it doesn’t dissolve in any liquid.
This is how silica high sand deposits are converted into glass with the help of high temperatures and other elements.
How Is a Quartz Crystal Used as an Abrasive?
As already discussed, sand deposits with a high quantity of silica come with a powerful rating of seven on the Mohs scale.
Quartz crystals are quite harder than other naturally occurring substances and are also found most abundantly in Earth’s crust. This is what makes them excellent abrasive material and Quartz sands can be used for:
- Sand blasting
- Scouring cleansers
- Grinding media
- Grit for sanding
How Is Quartz Used as A Foundry Sand?
Since Quartz is naturally extremely resistant to chemicals and heat, it becomes an excellent material to be used as foundry sand.
Quartz offers a high melting temperature that is considered to be higher than the majority of metals. Therefore, Quartz can easily be used for the molds and cores of common foundry work.
Quartz is most often used to refractory bricks that offer a high level of heat resistance and durability to homeowners and factory owners.
What Are Some Other Uses of Quartz Crystals?
Another amazing quality of quartz crystals is their ability to vibrate at specific frequencies without any trouble.
This is why you must have seen the word Quartz written on a lot of analog timepieces.
Quartz crystals can vibrate at specific frequencies in such an accurate manner that these can be used to make accurate time-keeping instruments and equipment without the need for any other electrical or mechanical component.
These quartz crystals are also used to transmit the majority of radio and television signals with amazing accuracy at stable frequencies, and that is why these are used for satellites and signal processing.
Back in the 1920s, crystal oscillators were created with the help of naturally found quartz crystals. These oscillators helped the soldiers keep accurate time and maintain constant radio communication with other soldiers on the battleground.
Nowadays, quartz crystals are used for:
- Analog watches
- Satellite radio transmitters
- Equipment that requires vibrational accuracy for performance
These quartz crystals are also used by the majority of modern manufacturers for the purpose of GPS meters and devices that can help pinpoint the right direction without any need for electrical components.
Quartz crystals are also used in lasers and help enhance the overall intensity of laser beams without breaking apart. This is because quartz crystals can tolerate a higher level of heat and chemical reactions without giving up.
How Many Different Varieties Exist for Quartz Crystals?
How Many Different Varieties Exist for Quartz Crystals?
This is a purple-colored variety of Quartz. These are quite similar to the natural crystalline form of Quartz, and offer almost the same attributes to the users.
- Aqua Aura
This form of Quartz is synthetically enhanced with the help of a coating. This coating is a father created from gold and other metals. The coating also gives a neon blue or other neon color to these crystals.
An opaque form of compact Quartz, it contains small mica, hematite, or goethite scales. These scales result in offering a glistening effect.
Aventurine is also classified as a rock because of its natural chemical composition oils quite similar to several minerals. However, the majority of scientists see this form as a variety of Quartz.
- Blue Quartz
As a blue variety of Quartz, it is most commonly used by faith healers to offer healing qualities to the users. It is highly uncommon in nature and rarely in crystal form.
- Cactus Quartz
This form of Quartz is basically a large crystal or a combination of different and multi-colored crystals overgrown with a layer of spiky smaller crystals.
That means that there are smaller and sharper crystals grown on top of the cactus quartz. Cactus Quartz can only be found in Boekenhouthoek (Magaliesberg) in South Africa.
One of the most common forms of Quartz, it’s a specific, microcrystalline form of Quartz. It is quite similar to naturally occurring Quartz in terms of chemical composition, and can also be viewed as Mica Crystals.
This form of Quartz is often found in yellow, orange, or brown colors. These can often be a combination of these colors.
- Faden Quartz
These are basically different groups of quartz crystals. These groups come with a white thread-like zone that runs through the interior vessels and veins of crystals.
The remaining layers of crystals are basically formed around the thread axis of the white-threaded zones and veins.
- Ferruginous Quartz
This form of Quartz comes with an opaque red to brown Hematite coating. These give off a neon-ish color scheme and often have internal inclusion.
- Herkimer Diamond
Noted as one of the most beautiful and lustrous forms of clear quartz crystals, it is a completely transparent form of quartz crystals. It comes specifically from the Herkimer Co. vicinity in the Mohawk Valley region of Central New York State.
- Milky Quartz
If you are looking for a white and translucent form of Quartz. It is also considered among the most beautiful and natural forms of Quartz, and it gives the transparent look of being milky white.
This is yet another opaque and translucent form of Quartz that primarily comes in black color. It is also referred to as smoky quartz due to its black color scheme.
- Phantom Quartz
It was named Phantom Quartz because it is known to grow internal phantom growths. These ghostlike layers are formed over hundreds of years within a crystal due to the remain of hot water solutions trapped inside cavities of pre-formed crystal.
These beautiful quartzes come in different colors ranging from light to emerald green. Moreover, these are also transparent or translucent, depending upon the natural composition of the surrounding rocks. The colors are also based upon the elements found in the surrounding regions.
If you want to take a look at some of the most beautiful and gorgeous light green and translucent forms of Quartz with Hedenbergite inclusions, Praseme is the one for you.
These are quite beautiful, and the color comes from the minerals found in the host rock. These quartz crystals are primarily found on Serifos Island, Greece.
These kinds of quartz crystals are artificially colored and come in a light green color scheme. These crystals are colored with the help of modern heat treatment of certain types of Amethyst crystals that can be found naturally in igneous rocks. These are also referred to as Green Amethyst Crystals.
- Rainbow Quartz
This form of quartz crystals is also known to be synthetically colored to appear rainbow-ish in nature.
It is synthetically colored with the help of heat treatment and made to look like an iridescent layer formed from gold or other metals. These are quite similar to aqua aura quartz crystals in terms of composition and color schemes.
- Rock Crystal
A colorless and transparent form of quartz crystals, it is most commonly found in the form of a large crystal and can be found in volcanic caves and igneous rocks that are over thousands of years old.
- Rose Quartz
This form of pink quartz crystals is also used by healthcare practitioners for a wide array of healthcare benefits and skin treatments. You must have heard the term rose quartz roller by beauty experts.
- Rutilated Quartz
If you are looking for the form of quartz crystals with golden yellow, needle-like rutile inclusions, the rutilated quartz crystals are the answer.
- Scepter Quartz
This form of quartz crystal basically comes with a scepter-like protrusion on the end of the crystal. This scepter-like protrusion is wider than the rest of the crystal, and can easily pierce through harsh surfaces without breaking apart.
- Smoky Quartz
These types of quartz crystals can be found in different color schemes ranging from brown to black. These darker color schemes often give these crystals a touch of smokiness.
- Star Quartz
This is a variety of quartz crystals exhibiting asterism in the form of a six-rayed star. These are also naturally polished on the exterior and contain a six-rayed star quality.
- Tourmalinated Quartz
These quartz crystals come with splintery tourmaline inclusions.
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What Is the Bottom Line Here?
Quartz Crystals are formed through a process known as the hydrothermal process, which involves hot water solutions, silica-rich minerals or rocks, and high pressures and temperatures. These quartz crystals are a result of the layer-by-layer addition of SiO2 molecules on the surface.
In general, when igneous rocks cool down, they form pockets that are filled with hot watery solutions. When these cool down, this results in a slow formation of crystals with the help of SiO2 molecules.
These quartz crystals are among the most commonly found minerals in the crust and are widely used in the production of glass, foundry sand, and other useful items.
Moreover, these crystals are also used for the purpose of oscillation and time-keeping, as these can vibrate at precise frequencies without getting disturbed.
TIP: Many people use the terms rock, mineral, crystal, stone, and gemstone interchangeably, but these terms have specific meanings in the world of rockhounds. Do you know what these terms mean? If not, check this article: