Quartz (SiO2) is a silicon oxide with a framework structure, a general term for α-quartz (low-temperature quartz, trigonal system) and β-quartz (high-temperature quartz, hexagonal system). The transition temperature of α-quartz and β-quartz is 573℃. When not specified, α-quartz is often referred to.

In the classification of mineral crystal chemistry, quartz belongs to the oxide class and the quartz family. Because quartz is in the end member position of silicates, it is sometimes also classified as a silicate. The quartz family includes SiO2 polymorphs such as quartz, cristobalite, tridymite, coesite, and stannite, among which coesite and stannite belong to high-pressure phases.

Theoretical chemical composition of quartz (wB%): SiO2 100, or Si 46.74, O 53.26. Natural quartz is relatively pure, but due to isomorphous substitution, it may contain a small amount of impurity elements such as Al, K, Na, Li, Ca, Fe, Mg, Mn, Ti, Cu, Zn, Cr, Ni, B, and P.

The framework-based crystal structure of quartz SiO2 determines that its structure is relatively open, with a relative density of 2.65, but the Si-O bond of the [SiO4] tetrahedron is strong, so the hardness is 7, acid-resistant (except HF), slightly soluble in KOH solution, high melting point (melting temperature 1710~1756℃), and it becomes quartz glass after cooling.

Quartz is a hard, wear-resistant, chemically stable silicate mineral. It is usually colorless or milky white, and can present different colors due to the mixing of various impurities. It is translucent, with a hardness of 7, brittle, no cleavage, shell-like fracture, oily luster, relative density of 2.65, optical rotation, piezoelectricity, poor heat transfer, non-conductive, and its electrical, thermal and some mechanical properties have obvious anisotropy.

Seven types of quartz mineral resources

Quartz is widely distributed in nature and has various causes, but currently there are seven types of quartz mineral resources that can be used for industrial applications: natural crystal, quartz sandstone, quartzite, vein quartz, powder quartz, natural quartz sand and granite quartz.

1.Natural crystal

A colorless and transparent large quartz crystalline mineral, the main component of which is silicon dioxide. The natural growth environment of crystal is mostly in caves, rock cracks or joints, faults, and its growth conditions are relatively harsh. Four conditions must be met at the same time: sufficient growth space, the ability to provide hydrothermal fluids rich in silicon dioxide, a certain temperature and pressure, and sufficient growth time.

2.Quartz sandstone

Quartz sandstone is a consolidated sandy sedimentary rock. Its quartz and siliceous debris content is generally >95%, and the accessory minerals are mostly feldspar, mica and clay minerals. There are very few heavy minerals, and the cement is generally siliceous.

3.Quartzite

Quartzite is a metamorphic rock formed by regional metamorphism or thermal contact metamorphism of quartz sandstone or other siliceous rocks. In addition to feldspar, mica and clay minerals, the associated minerals often contain trace amounts of tourmaline, hematite and zircon. Compared with quartz sandstone, its ore is dense and hard, with higher hardness. my country's quartz resources are very rich, and the amount of development and utilization is large.

4.Vine quartz

It is mainly formed by magmatic hydrothermal action related to granite. It has a dense block structure and a single mineral composition, almost all of which is quartz. The SiO2 content is generally above 99%. Vein quartz deposits are generally small in scale, steep in occurrence, generally a few meters to tens of meters in thickness, and generally tens of meters to hundreds of meters in length. A mining area can be composed of one or more veins.

5.Powder quartz

It is a natural powdered quartz ore with extremely fine particles and high SiO2 content. It is mainly a sedimentary weathering deposit formed by the weathering and disintegration of siliceous parent rock. Under special geological conditions, under the influence of factors such as warm and humid paleoclimate, flat terrain and paleogeography, siliceous rocks are constantly broken and disintegrated, and impurities are taken away by hydraulic force, eventually forming a deposit.

6.Natural quartz sand

It is a sandy quartz mineral raw material with quartz as the main mineral component, formed by long-term weathering of parent rocks such as granite, quartzite, quartz sandstone and vein quartz in nature. Its associated minerals include feldspar, rock fragments, mica, clay minerals and heavy minerals such as zircon, tourmaline, ilmenite and amphibole. It is mainly marine sedimentary sand deposits and river-lake sedimentary sand deposits. Common areas include Tongliao, Inner Mongolia, Jinjiang, Fujian, Wenchang, Hainan, etc.

7.Granite quartz

The fundamental reason why Sibelco IOTA high-purity quartz series products can obtain an international monopoly is that it has the world's unique high-purity quartz high-quality raw material discovered so far - granite quartz. The raw material is pegmatite granite from the Spruce Pine area of North Carolina, USA. The discovery of this special type of quartz deposit is quite legendary.

The mine was originally used to produce feldspar and muscovite, and quartz was a waste product in the tailings. In the 1970s, due to the depletion of crystal, the raw material of quartz glass, finding natural quartz that could replace crystal became a problem that many countries urgently needed to overcome at that time. In this context, after improving the flotation technology, quartz in granite pegmatite was used to replace crystal to produce high-purity quartz sand. To this day, the United States still monopolizes the international market for high-end high-purity quartz sand products.

Typical applications of quartz

The application of quartz is very extensive. After a series of production and processing processes, it is used in many traditional and emerging industries such as glass industry, foundry industry, ceramic industry, refractory industry, chemical industry, oil extraction, water purification materials, building materials, new energy photovoltaics, electronic semiconductors, optical fibers, optics, electric light sources, high-end fiber materials, industrial fillers, etc.

The glass industry is the largest application field

The glass industry is the field with the largest consumption of quartz resources. It is widely used in construction, automobiles, new energy, medical and other fields. The main product types of the glass industry include flat glass, utensil glass, tempered glass, photovoltaic glass, electronic glass, medicinal glass, etc.

High-end semiconductor field

Semiconductor field: The core link of semiconductor integrated circuit manufacturing is the chip manufacturing link. Chip manufacturing mainly consists of four parts: single crystal growth, wafer processing and manufacturing, integrated circuit chip production and post-packaging. Among them, the most core, most difficult and most demanding for related materials are silicon wafer manufacturing and wafer process links.

The application of quartz in the semiconductor field is mainly semiconductor-grade quartz crucibles and auxiliary materials for wafer manufacturing. Quartz products run through the silicon wafer manufacturing and wafer processing links, and are used in key processes such as semiconductor support diffusion, oxidation, deposition, and etching. Among them, high-purity quartz sand with a purity of 5N2 can be used to make semiconductor quartz crucibles, and high-purity quartz sand with a purity of 4N and 4N8 can be used to make quartz materials for silicon wafer oxidation and diffusion.

Popular application areas

In recent years, the "new three" represented by new energy vehicles, lithium batteries, and solar photovoltaic cells have added new highlights to China's manufacturing, and have performed particularly well in the export market, providing new momentum for China's high-quality economic development.

In the photovoltaic industry chain, quartz products play a pivotal role. In addition to photovoltaic glass produced with ultra-white low-iron quartz sand as raw material, quartz crucibles produced with high-purity quartz sand as raw material are the most eye-catching products in the downstream application field of quartz in recent years.

Quartz crucibles are a subdivided product of quartz glass products, with properties such as cleanliness, homogeneity, and high temperature resistance. At present, it is widely used in the production process of refining crystalline silicon in the fields of solar energy and semiconductors, and is a consumable in the production process of crystalline silicon.

Compared with ordinary quartz sand, high-purity quartz sand prepared by mineral processing and refining has better high temperature resistance and thermal stability. As the core raw material of quartz crucibles, the purity of quartz sand is the core indicator to ensure the excellent performance of quartz crucibles.