What is Silica?

Silica (chemical name for the mineral quartz and a synonym for silicon dioxide): Used in manufacture of special steels and cast iron, aluminum alloys, glass and refractory materials, ceramics, abrasives, water filtration, component of hydraulic cements, filler in cosmetics, pharmaceuticals, paper, insecticides, rubber reinforcing agent - especially for high adhesion to textiles, anti-caking agent in foods, flatting agent in paints, thermal insulator. Fused silica is used as an ablative material in rocket engines, spacecraft, silica fibers used in reinforced plastics.

Silica History & General Information

For any mineral or group of minerals there are two general classes of facts to be ascertained: (1) the geometrical, physical, and chemical properties; (2) the mode of occurrence, association, and origin, or briefly what may be called the natural history of the mineral.
To the geologist, of course, the natural history of a mineral is its most attractive feature, but until the mineral is accurately defined and determined, the significance of its occurrence and origin may be lost sight of.
It is my purpose to discuss the various silica minerals. The silica minerals are with a single exception accurately defined; they have been produced in the laboratory; they constitute the most complete example of polymorphism known. They are, moreover, of considerable geological interest, and altogether we have a fairly good idea of the role that the silica minerals play in Nature.
Let us first consider briefly the silica minerals and their properties as a background for the discussion of their natural history.
The name silicon comes from the Latin word silicis which means flint.
Silicon is the second most common element in the Earth's crust, comprising 25.7% of the Earth’s crust by weight. It was discovered in 1824 by the Swedish chemist Jons Jakob Berzelius. It is shiny, dark gray with a tint of blue. Silicon, atomic number of 14, is a semi-metallic or metalloid, because it has several of the metallic characteristics. Silicon is never found in its natural state, but rather in combination with oxygen as a silicate ion (SiO4) in silica-rich rocks such as obsidian, granite, diorite, and sandstone. Feldspar and quartz are the most significant silicate minerals. Silicon alloys with a variety of metals, including iron, aluminum, copper, nickel, manganese and ferrochromium.
Silica is processed into two intermediate products- silicon and ferrosilicon. Silicon is known in the ferroalloy and chemical industries as “silicon metal.” The ultra pure form of silicon (>99.99% Si) is distinguished from silicon metal by the term “semiconductor-grade silicon.” The terms “silicon metal” and “silicon” are used interchangeably.
Silicon is used in ceramics and in making glass. Ferrosilicon is crushed into a variety of forms and sold as bulk metal. Depending on its intended use, it can be mixed with aluminum and calcium. It is a very heavy alloy. When it comes into contact with moist air or water, an explosive chemical reaction occurs in which hydrogen is released. Consequently there are very strict laws about the shipping of ferrosilicon it must be kept perfectly clean and dry.


<= A quartz crystal.
Silicon is considered a semiconductor. This means that it conducts electricity, but not as well as a metal such as copper or silver. This physical property makes silicon an important commodity in the computer manufacturing business.
Silica is in human connective tissues, bones, teeth, skin, eyes, glands and organs. It is a major constituent of collagen which helps keep our skin elastic, and it helps calcium in maintaining bone strength. Silica dust in mines has caused silicosis or a lung disease in miners. Wetting the area being mined and application of good ventilation has reduced the danger of lung disease. Some organisms like sponges and some plants use silicon to create structural support.

Silica Sources

Silicon compounds are the most significant component of the Earth’s crust. Silicon is recovered from an abundant resource: sand. Most pure sand is quartz, silicon dioxide (SiO₂). Since sand is plentiful, easy to mine and relatively easy to process, it is the primary ore source of silicon. Some silicon is also retrieved from two other silicate minerals, talc and mica. The metamorphic rock, quartzite, is another source (quartzite is metamorphosed sandstone). All combined, world resources of silicon are plentiful and will supply demand for many decades to come.
Iran has plentiful sand, quartzite, talc and mica resources.

Silica Substitutes and Alternative Sources

There are relatively few options to replace silicon in its applications. Germanium and gallium arsenide can be used as semiconductors in place of silicon. In some applications, a small number of metal alloys, such as silicomanganese and aluminum, can substitute for ferrosilicon.

Silica Packing

All grades of Silica are available in various types of packaging
1. 1 Ton Jumbo bags
2. 25kg package for powder

Low Quartz Though by no means the most common, quartz is probably the best known of all minerals. The ancient Greeks called it crystallus, in the belief that it was permanently congealed water, and thus was derived our word crystal.
Quartz has been investigated from almost every standpoint, and its physical constants have been very accurately determined. The symmetry of law quartz is trigonal trapezohedral (A3 • 3A2). Twinned crystals of quartz are not uncommon.

High Quartz On heating quartz, Le Chatelier, the French chemist, noticed a rapid change in some of its properties at a temperature of about 570°C. This has been confirmed by subsequent investigators, and Wright and Larsen place the inversion point at 575°±2°C. At this temperature there is a sudden change in the properties, which means that a new substance is produced. The new substance is hexagonal trapezohedral, with the symmetry A6•6A2. It has been called high quartz to distinguish it from the ordinary form which is law quartz. The difference in symmetry of the two forms is shown by Laue X-ray photographs, which means that there is a difference in the arrangement of the atoms or molecules in the two cases. The crystal habit of high quartz is usually short and stumpy with narrow prism faces (Plate 1, Fig. 1) in contrast with the prismatic habit of law quartz.

Chalcedony The microcrystalline form of silica known as chalcedony is very much like law quartz in its properties, but seems to be somewhat different from law quartz. It does not appear to grade into quartz, and may easily be distinguished from it in practically all cases.
Whether chalcedony is a distinct form of silica or simply a variety of quartz is uncertain.
A reasonable explanation is that chalcedony is an aggregate of silica fibers which are oriented in one direction only. In quartz the fibers are oriented in all directions. This assumes the thread structure advocated by Sosman.3

OpalOpal is a hydrogel mineral of colloidal origin. In some specimens we have evidence of its origin by desiccation of a gelatinous mass of silica. Opal is probably a solid solution of water in silica. When first formed it consists of two phases, silica and water, but in time the water gradually diffuses into the silica and a solid solution is formed. Opal is not, then strictly speaking, a colloid, but only colloidal in origin.
Opal is apparently one of the few strictly amorphous minerals, since it gives no X-ray diffraction pattern.

Lechatelierite The latest of the silica minerals to be described is lechateliérite, named by Lacroix in 1915 in honor of Henry Le Chatelier, the famous French chemist, whose work on silica and silicates is well known. Lechateliérite is naturally occurring silica glass. It has not been generally recognized as a distinct mineral.
In its properties lechateliérite is much like opal, but in origin it is absolutely different. As Miers has well said: "The essential characters of a mineral, moreover, are quite independent of its source or previous history . . . . ." This statement is important for crystalline minerals, but is probably not valid for amorphous substances such as opal and lechateliérite. At any rate, it is convenient to treat these two as distinct minerals. About a century ago Breithaupt distinguished two classes of amorphous substances, the hyaline or glasses and the porodine or those of colloidal origin. It is unfortunate that the term hyalite has been used as a variety of opal.
Lechateliérite is unique in that it is the only naturally occurring glass that is definite enough to be considered a mineral.
Silica glass, which is often incorrectly called "quartz glass", is now made on a commercial scale in a very pure transparent form. Silica glass possesses some unusual physical properties such as transparency to ultraviolet light and a remarkably small coefficient of thermal expansion. A rod of the glass 1 meter in length will expand only about 0.6 mm. for a rise of temperature of 1000°C.
The Silica Minerals In General
All the known forms of silica, and they are legion in number, are believed to be synonyms or varieties of the ones mentioned. Asmanite, found in meteorites, is a synonym of tridymite. Lussatite, considered by some to be distinct form, is probably a mixture of opal and fibrous chalcedony.
It seems probable that all the forms of silica capable of existence at atmospheric pressures are now known. But it is not safe to say that all the possible distinct forms of silica are known, for polymorphism is a general phenomenon of nature and there is no theoretical limit to the number of polymorphous modifications of any chemical substance.
The artificial production of the various forms of silica under specified conditions in the laboratory has been a great help in the proper understanding of their natural history.
Let us next consider the typical modes of occurrence of the various silica minerals with a view of determining, as far as possible, the conditions under which they were formed in nature.

Occurrence Of Opal Opal is a late secondary mineral found in seams and cavities of various rocks, especially of volcanic igneous rocks. It is found in sedimentary beds which are in part at least formed from diatoms, radiolaria, and sponge spicules.
It seems plausible to regard opal as a mineral which has formed rapidly. Our information concerning the formation of minerals of colloidal origin is rather meager.

Occurrence Of Low Quartz Low quartz is a typical hydrothermal mineral which is probably always formed below 575°C. Its temperature range is considerable. Its occurrence as secondary enlargements of sand grains in sandstones as well as numerous occurrences in sedimentary rocks proves that it may be formed at temperatures at little above the ordinary. Vein quartz usually has a prismatic habit.

High quartz is the original mineral of persilicic igneous rocks present because there is an excess of silica left over after the affinities of silica for the various oxides are satisfied. At atmospheric pressure under laboratory conditions it is formed above 575°C. But in nature it has probably been formed at lower temperatures because of the influence of mineralizers. 575°C.As a point on the geological thermometer cannot be accepted too literally.
High quartz usually shows a bipyramidal habit due to the minor development of the prism faces.

Transformations of the Silica Minerals When the silica minerals are studied in the laboratory, there are found to be two types of inversion:
1) Inversions of the law and high forms of quartz, tridymite, and cristobalite respectively, which take place rapidly.
2) Inversions of quartz, tridymite, and cristobalite from one into another. - These inversions are sluggish, and so are of geological importance.
The inversion temperatures of the various polymorphous forms of silica have been determined under laboratory conditions by the Geophysical Laboratory.
These laboratory experiments are of course extremely important, but the mineralogist and petrographers are primarily interested in the natural occurrences and transformations.
I next wish to present the results of my study of some of the natural transformations of the silica minerals.

Average Composition of the Crust

Eight elements combine to make most minerals and rocks found in the Earth's crust. The elements are oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. The letters in the parentheses are abbreviations. You may already be somewhat familiar with some forms of these elements. Silicon combines with two atoms of oxygen (in the nomenclature of chemist, SiO₂, or silica) to make the mineral quartz, which is common on many mainland beaches. Silica is also used for window glass. Aluminum is used for soda cans. Iron is used for the frame of automobiles and reacts with oxygen in the air to produce rust. Magnesium is used in flares. Calcium is a major component in our teeth and bones. Sodium is in table salt. Potassium is used in fertilizer. Titanium is combined with other metals to produce alloys, which are stronger metals.

This definition excludes the thousands of compounds invented by humans in laboratories because these compounds are not naturally occurring. Compounds that are found in only plants or animals are also excluded. Liquids are excluded because they are not crystalline; their atoms are free to move. Minerals can be a single element, like diamond, which is made of carbon of compounds of two or more elements, like quartz, which contains one silicon and two oxygen atoms. Definite composition indicates that a chemical analysis of a given mineral will always produce the same ratio of elements. For example, quartz will always have one silicon for every two oxygen atoms. Therefore, minerals can be expressed by chemical formulas, such as SiO₂ for quartz.

Crystalline Silica

Industrial sand, also called silica sand, contains a very high percentage of silica, in the form of quartz, and is distinguished by its high degree of purity. Industrial sand deposits are thus less common than deposits mined for construction sand and gravel. Industrial sand is derived from hard rock quartzite formations and in unconsolidated beds of silica sand.
Industrial sand must meet stringent quality requirements since it is used as the principal ingredient in the manufacture of glass, and in foundry cores and molds for metal castings. Industrial sand also is an ingredient in paints, refractory products and specialty fillers. It is used in water filtration, abrasives, for enhancing production of oil and gas, and in specialty construction applications.
Industrial sand also satisfies recreational needs, such as golf courses, tennis courts and ball fields. It is used in municipal water filtration, in residential pool filters and sand boxes. Because of the ubiquitous occurrence and many commercial uses of silica, potential exposure to silica dust is widespread.

Occupational exposure to crystalline silica occurs by breathing silica-containing dusts present in many industries, such as: mining and quarrying; steel, iron, and other metal foundries; abrasive blasting; construction; glass and ceramics; paint and pigments; and, quarrying and crushing stone.

Silicosis A commonly known health hazard which has been associated historically with the inhalation of silica-containing dusts is silicosis. Silicosis is a fibrotic lung disease (development of scar tissue in the lungs) which can be progressive and disabling; it can lead to death. It is the primary health risk from breathing silica and the oldest known occupational disease. To pose a danger to the lungs, a dust particle must be respirable. A dust particle is considered respirable if it is smaller than 10 micrometers, about four-ten thousandths of an inch. Dust particles that are respirable are capable of being inhaled into the conducting airways and gas exchange regions of the lungs. Dust particles larger than 10 micrometers are not capable of penetrating the defense mechanisms of the lung to produce injury to the important lower regions of the lung where oxygen transfer takes place.
There are three different types of silicosis. Chronic silicosis may result from prolonged inhalation of excessive levels of respirable silica dust, and may take many years of exposure to develop. A second type, accelerated silicosis, may occur in a relatively shorter period of time from the inhalation of intense excessive levels of respirable silica dust. Acute silicosis, the third type, develops rapidly and has been reported in occupations such as sand blasting and drilling through silica-containing rock. Cases of acute silicosis and complicated cases of chronic silicosis and accelerated silicosis can be fatal.
The number of cases of silicosis can be reduced by implementing measures to reduce exposure to silica-containing dusts. Such measures include engineering controls, improved work practices, training programs, and respiratory protection programs.

Workplace Safety

Silica Usage

Recommended Filled of Application