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Albite

earth science Maturity 7-9 Next article →

Albite is a significant mineral belonging to the plagioclase feldspar group. It serves as the sodium endmember of the plagioclase solid solution series. This means it is the version of the mineral characterized by high sodium content. Specifically, albite contains less than 10% anorthite. Anorthite is another mineral within the same series. Because of its chemical makeup, albite is classified as a tectosilicate. This term describes a type of silicate mineral with a framework structure. Most albite crystals appear pure white. This color is the reason for its name, which comes from the Latin word "albus."

Albite-70858
Albite-70858

The physical structure of albite is quite distinct. It crystallizes in the triclinic system, which refers to its crystal shape. This shape is often described as pinacoidal forms. Albite almost always shows crystal twinning. This phenomenon creates minute parallel striations, or tiny lines, on the crystal faces. The mineral has a specific gravity of approximately 2.62. It also possesses a Mohs hardness of 6 to 6.5. These measurements help geologists identify the mineral in the field.

Albite-70858
Albite-70858

As albite cools, it can undergo a process called exsolution. This process creates interesting visual patterns within the mineral. During exsolution, fine parallel segregations form. These segregations often alternate with pink microcline. This results in a specific variety known as perthite. The way the mineral cools directly dictates these internal structures. Such details provide clues about the history of the rock where the albite is found.

Albite-70858
Albite-70858

There are two primary variants of albite: low albite and high albite. High albite is also referred to as analbite. While both are triclinic, they differ in their unit cell volume. The unit cell is the smallest repeating unit of the crystal structure. In high albite, this volume is slightly larger. You can transform low albite into high albite by heating it. High albite is often found in specific environments like meteor impact craters. One such location is the Winslow crater in Arizona.

Albite-70858
Albite-70858

Further heating can change the mineral even more. If you heat albite above 600 degrees Celsius, its symmetry changes. It shifts from a triclinic structure to a monoclinic structure. This specific variant is known as monalbite. The chemical composition can also shift slightly. Sometimes, potassium can replace the sodium in the mineral. This can happen in amounts up to 10%. If the potassium exceeds this 10% limit, the mineral is called anorthoclase instead.

Albite-70858
Albite-70858

Albite is found in many different geological settings. It occurs in granitic and pegmatite masses. In these masses, it often appears as a variety called cleavelandite. It is also found in hydrothermal vein deposits. Additionally, it forms part of the greenschist metamorphic facies. This facies describes rocks that were originally basaltic in composition. Albite is frequently found alongside other minerals. Common associates include biotite, hornblende, orthoclase, muscovite, and quartz.

Albite-70858
Albite-70858

The history of albite discovery began in 1815. It was first reported in Finnbo, located in Falun, Dalarna, Sweden. Later, a new variety was identified in 1925. An academician named Alexander Fersman discovered an iridescent version. He found this variety near the White Sea coast. This iridescent albite is known by the trade name belomorite. Today, albite has several practical uses. It is used as a semiprecious gemstone. It is also used industrially to manufacture glass and ceramics. Geologists continue to use it as a vital tool for identifying rock types.

Albite-70858
Albite-70858
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