Silicates Minerals

Wollastonite is a group of innosilicate mineral, formula is CaSiO3 that may inlude small amount of magnesium, manganese and iron substituting for calcium. A...

Hornblende is a inosilicate amphibole minerals, which are two type hornblende minerals. They are ferrohornblende and magnesiohornblende. They are an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate.

Plagioclase is series of framework silicate minerals in feldspar group. Plagioclase is a continuous series of solid solutions known as the plagioclase feldspar series,...

A light mica, lepidolite is Earth’s most common lithium-bearing mineral. Its name is derived from two Greek words: lepidos, which means “scale,” and lithos, which means “stone.” Although typically pale lilac, specimens can also be colorless, violet, pale yellow, or gray. Lepidolite crystals may appear pseudohexagonal. The mineral is also found as botryoidal or kidneylike masses and fine- to coarse-grained, interlocking plates. Its perfect cleavage yields thin, flexible sheets. Lepidolite occurs in granitic pegmatites, where it is associated with other lithium minerals, such as beryl and topaz. The mineral is economically important as a major source of lithium, which is used to make glass and enamels. It is also a major source of the rare alkali metals rubidium and cesium.

The most common pyroxene, augite is named after the Greek word augites, which means “brightness”—a reference to its occasional shiny appearance. Most augite has a dull, dark green, brown, or black finish. Augite occurs chiefly as short, thick, prismatic crystals with a square or octagonal cross section and sometimes as large, cleavable masses. It occurs in a solid-solution series in which diopside and hedenbergite are the end-members. Augite is common in silica-poor rocks and various other dark-colored igneous rocks, as well as igneous rocks of intermediate silica content. It also occurs in some metamorphic rocks formed at high temperatures (1,065°F/575°C or above). Augite is a common constituent of lunar basalts and some meteorites. Notable crystal localities are in Germany, the Czech Republic, Italy, Russia, Japan, Mexico, Canada, and USA. Because it is difficult to distinguish between augite, diopside, and hedenbergite in hand specimens, all pyroxenes are often identified as augite.

The Glaucophane mineral is named after two Greek words: glaukos, which means “bluish green”; and phainesthai, which means “to appear.” Specimens can be gray, lavender blue, or bluish black. Crystals are slender, often lathlike prisms, with lengthwise striations. Twinning is common. Glaucophane can also be massive, fibrous, or granular. When iron replaces the magnesium in its structure, it is known as ferroglaucophane. Glaucophane occurs in schists formed by high-pressure metamorphism of sodium-rich sediments at low temperatures (up to 400°F/200°C) or by the introduction of sodium into the process. Glaucophane is often accompanied by jadeite, epidote, almandine, and chlorite. It is one of the minerals that are referred to as asbestos. Glaucophane and its associated minerals are known as the glaucophane metamorphic facies. The presence of these minerals indicates the range of temperatures and pressures under which metamorphism occurs.

The name anthophyllite comes from the Latin word anthophyllum, which means “clove”—a reference to the mineral’s clove-brown to dark brown color. Specimens can also be pale green, gray, or white. Anthophyllite is usually found in columnar to fibrous masses. Single crystals are uncommon; when found, they are prismatic and usually unterminated. The iron and magnesium content in anthophyllite is variable. The mineral is called ferroanthophyllite when it is iron-rich, sodium-anthophyllite when sodium is present, and magnesioanthophyllite when magnesium is dominant. Titanium and manganese may also be present in the anthophyllite structure. Anthophyllite forms by the regional metamorphism of iron- and magnesium-rich rocks, especially silica-poor igneous rocks. It is an important component of some gneisses and crystalline schists and is found worldwide. Anthophyllite is one of several minerals referred to as asbestos.

This member of the sodium- and potassium-rich feldspar group takes its name from the Greek word anorthos, which means “not straight”—a reference to its oblique cleavage. Anorthoclase is colorless, white, cream, pink, pale yellow, gray, or green.

Used in ceramics and as a mild abrasive, microcline is one of the most common feldspar minerals. It can be colorless, white, cream to pale yellow, salmon pink to red, or bright green to blue-green. Microcline forms short prismatic or tabular crystals that are often of considerable size: single crystals can weigh several tons and reach yards in length. Crystals are often multiply twinned, with two sets of fine lines at right angles to each other. This gives a “plaid” effect that is unique to microcline among the feldspars.

A member of the solid-solution series of potassium and sodium feldspars, sanidine is the high-temperature form of potassium feldspar, forming at 1,065°F (575°C) or above. Crystals are usually colorless or white, glassy, and transparent, but they may also be gray, cream, or occur in other pale tints.

An important rock-forming mineral, orthoclase is the potassium-bearing end member of the potassium sodium feldspar solid-solution series. It is a major component of granite its pink crystals give granite its typical color.

Talc is a naturally occurring mineral known for its softness, smoothness, and ability to absorb moisture. It is a silicate mineral that is composed...