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What is Limonite?
Before modern mineral analysis, the name “limonite” was given to many of the yellowish to yellowish brown iron oxides produced during the weathering of iron-bearing rocks or deposited as bog, lake, and shallow marine sediments. Researchers who studied “limonite” discovered that it is amorphous and has a variable composition. It often contains significant amounts of…
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Hardness and Use as an Abrasive
The extreme hardness of corundum makes it especially useful as an abrasive. Crushed corundum is processed to remove impurities and then screened to produce uniformly sized granules and powders. These are used for grinding media, polishing compounds, sand papers, grinding wheels, and other cutting applications. Some problems with using natural corundum as an abrasive are…
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Geologic Occurrence of Corundum
Corundum is found as a primary mineral in igneous rocks such as syenite, nepheline syenite, and pegmatite. Some of the world’s most important ruby and sapphire deposits are found where the gems have weathered from basalt flows and are now found in the downslope soils and sediments. Corundum is also found in metamorphic rocks in locations where aluminous shales or bauxites have…
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Properties of Corundum
Corundum is an exceptionally hard and tough material. It is the third-hardest mineral, after diamond and moissanite. It serves as the index mineral for a hardness of nine on the Mohs Hardness Scale. Its hardness, high specific gravity, six-sided crystals and parting are very good diagnostic properties to use in its identification. A summary of the physical properties…
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Other Uses of Silver
Other traditional uses of silver exist. For example, silver is one ingredient in the amalgam used to fill dental cavities, though this approach has been largely replaced by other materials due to the presence of toxic mercury in the amalgam. Silver has also been used to plate instruments, such as flutes. Today, silver is being…
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Uses of Silver for Water, Food, Hygiene
Silver’s antibacterial properties have been applied for thousands of years, long before the discovery of microbial organisms, because silver containers and coins were known to prevent spoilage of liquids. Today, a silver coating prevents bacterial build-up in carbon-based water filters, while silver ions in water purification systems carry oxygen that oxidizes and kills microbes. Silver-copper…
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Uses of Silver in Awards
Due to its status as a precious metal, ranked second only to gold, silver is often used to award second place. The most famous silver award is the second-place Olympic Silver Medal. Silver also symbolizes honor, valor, and accomplishment, which is why many military organizations, employers, clubs, and associations use silver or silver-colored awards to…
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Uses of Silver in Engines
Engine bearings rely on silver. The strongest bearing is made from steel that has been electroplated with silver. Silver’s high melting point allows it to withstand the high temperature of engines. Silver also acts like a lubricant to reduce friction between a ball bearing and its housing. Due to its ability to absorb oxygen, silver…
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Uses of Silver in Mirrors and Glass
Silver is almost completely reflective when polished. Since the 19th century, mirrors have been made by coating a transparent glass surface with a thin layer of silver, though modern mirrors also use other metals like aluminum. Many windows of modern buildings are coated with a transparent layer of silver that reflects sunlight, keeping the interior…
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Uses of Silver in Medicine
Silver ions act as a catalyst by absorbing oxygen, which kills bacteria by interfering with their respiration. This antibiotic property, along with its non-toxicity, has given silver an essential role in medicine for thousands of years. Before widespread use of antibiotics, silver foil was wrapped around wounds to help them heal, and colloidal silver and…