Aluminum silicate, also known as aluminium silicate, is a mixture of aluminum, silica, and oxygen that can be either a mineral, or combined with water to form a clay. It can also combine with other elements to form various other minerals or clays. Some of these forms are used medicinally and industrially, and they retain their strength at high temperatures — a property known as being refractory. Others are used as gemstones.
This mineral comes in three different forms: kyanite, andalusite, or sillimanite. They all have the chemical formula Al2SiO5, but they have different crystal structures. All three forms are rarely found in the same rock, because each occurs under different conditions of pressure and temperature. Only kyanite and sillimanite are used industrially.
Kyanite is unusual in that its hardness varies, depending on the direction of the crystals. Some of the crystals are similar to blue sapphires and are used as gemstones. Kyanite is also used in the making of the frequently used industrial compound mullite. This compound has the chemical formula 3Al2O3.2SiO2. It is used as a refractory in the ceramics industry and in the manufacture of many things, including high voltage electrical insulations, glass, and heating elements.
Sillimanite can also be used as a refractory. It is used in a variety of industries, including glass-making, ceramics, cement, iron foundries, and metal smelting.
Aluminum silicate can be hydrated, or have water molecules associated with it, in which case, it forms a clay. Kaolin is the term for a group of clay minerals with the chemical formula of Al2O3.2SiO2.2H20. It forms a layer of two alternating crystals — one of silicon-oxygen and one of alumina. Kaolinite is the main constituent of kaolin.
Kaolin has been used for many years to control diarrhea and to dry poison ivy and poison oak rashes. It has also been used to treat diaper rash. Commercially, it has been important in the ceramics industry, particularly for the production of fine porcelain. It is also used to manufacture cement, bricks, and insulators, among other things.
Another compound found as a mineral and as a clay is magnesium aluminum silicate, which is composed of magnesium, aluminum, silica, and oxygen. In its mineral form, it is a type of garnet called pyrope, which is often used as a gemstone, and it is the only garnet to always be red in color. Its chemical formula is Mg3Al2(SiO4)3, although there are frequently trace amounts of other elements present.
The hydrated form is a mixture of clays, and this purified mixture is commonly used as an antacid. It is also used as a thickener in beauty products and cosmetics, and as an inactive ingredient in deodorants.
Sodium aluminum silicate is also referred to as sodium aluminosilicate and is composed of sodium, aluminum, silica, and oxygen. Two minerals of this type are albite and jadeite. Albite has the chemical formula of NaAlSi3O8, while that of jadeite is NaAlSi2O6. Albite is common in Earth’s crust, and breaks down under pressure to form jadeite and quartz. Jadeite is one of the types of minerals that make up the gemstone jade.
There is an industrial form of sodium aluminosilicate, known as synthetic amorphous sodium aluminosilicate, that contains water. This is a series of compounds and does not have a fixed chemical composition. It is used as an additive in powdered foods to keep lumps from forming.
Synthetic zeolites are prepared from this compound. These are minerals that are very porous and are used commercially as adsorbents. They are used primarily as laundry detergents, although they have a variety of other industrial uses.