Cassiterite
Tin oxide mineral, chief tin ore since ancient times.
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Cassiterite is a tin oxide mineral with the chemical formula SnO2. It is generally opaque, though it becomes translucent when found in thin crystals. The mineral’s luster and its multiple crystal faces make it a desirable gemstone. Cassiterite was the chief tin ore throughout ancient history and remains the most important source of tin today.
Etymology
It also possesses semiconducting properties. The name derives from the Greek word “kassiteros,” meaning tin, a term that appears in Homer’s Iliad in the description of the Shield of Achilles. Ancient etymological attempts include Pliny the Elder’s mention that the Greeks called tin “cassheros,” and Stephanus of Byzantium’s reference to an island named Kassitera from which tin came. Modern scholarship suggests the word may have Elamite origins, possibly related to the Babylonian “kassi-tira” or the region of the Kassites, an ancient people of west and central Iran.
Occurrence
Most current sources of cassiterite come from alluvial or placer deposits, where the weathering-resistant grains accumulate. The best primary deposits are found in the tin mines of Bolivia, occurring in crystallized hydrothermal veins. Rwanda has an emerging cassiterite mining industry, while fighting over deposits in eastern parts of the Democratic Republic of the Congo, particularly in Walikale, has led to cassiterite being classified as a conflict mineral.
Cassiterite is a widespread minor constituent of igneous rocks. The Bolivian veins and the ancient workings of Cornwall and Devon, England—dating back 4,500 years—are concentrated in high-temperature quartz veins and pegmatites associated with granitic intrusives. These veins often contain tourmaline, topaz, fluorite, apatite, wolframite, molybdenite, and arsenopyrite.
In Cornwall, surface deposits on Bodmin Moor show traces of a hydraulic mining method called streaming. Major tin production today also comes from placer deposits in Malaysia, Thailand, Indonesia, the Maakhir region of Somalia, and Russia. Hydraulic mining concentrates the ore, relying on cassiterite’s high specific gravity of about 7.0.
Crystallography
Crystal twinning is common, with most aggregate specimens showing twins, typically bent at a near-60-degree angle to form an “elbow twin.” Botryoidal or reniform cassiterite is called wood tin. Quality crystals are used as gemstones and for collector specimens.
Lore & Background
It is generally opaque, but thin crystals can be translucent. Its luster and multiple crystal faces make it desirable as a gemstone. The mineral has a high specific gravity of about 7.0, a property exploited in hydraulic mining methods used to concentrate the ore. Crystal twinning is common, with many aggregate specimens showing twins bent at a near-60-degree angle, known as "elbow twins." Botryoidal or reniform varieties are called wood tin.
Cassiterite is also a semiconductor. It was the chief tin ore throughout ancient history and remains the most important source of tin today. Most current sources come from alluvial or placer deposits, as the grains are resistant to weathering.
Primary cassiterite is found in crystallized hydrothermal veins, notably in the tin mines of Bolivia. Other significant deposits occur in high-temperature quartz veins and pegmatites associated with granitic intrusives, such as the ancient workings of Cornwall and Devon, England, which date back 4,500 years. Major placer deposits are found in Malaysia, Thailand, Indonesia, the Maakhir region of Somalia, and Russia. Rwanda has an emerging mining industry, while fighting over deposits, particularly in Walikale, is a major cause of conflict in eastern Democratic Republic of the Congo, leading to its classification as a conflict mineral.
Reader's Guide
Cassiterite's significance lies in its role as the dominant source of tin from ancient times to the present. It occurs in alluvial or placer deposits due to its weathering resistance and high specific gravity (about 7.0), which facilitates hydraulic mining concentration. Primary deposits are found in high-temperature quartz veins and pegmatites associated with granitic intrusives, notably in Bolivia and the historic mines of Cornwall and Devon, England.
The mineral is also a conflict mineral, as fighting over cassiterite deposits in eastern Democratic Republic of the Congo, particularly in Walikale, has fueled regional conflict. Beyond ore, cassiterite is used as a gemstone and collector specimen, and its crystal twinning—often forming 'elbow twins'—is characteristic. Botryoidal or reniform varieties are called wood tin.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Cassiterite (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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