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Physical Properties of Ilmenite
Ilmenite is a black mineral with a submetallic to metallic luster. With just a glance it can easily be confused with hematite and magnetite. The differentiation is easy. Hematite has a red streak, while ilmenite has a black streak. Magnetite is strongly magnetic, while ilmenite is not magnetic. Occasionally ilmenite is weakly magnetic, possibly from small amounts of included magnetite.…
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Chemical Composition of Ilmenite
Ilmenite’s ideal chemical composition is FeTiO3. However, it often departs from that composition by containing variable amounts of magnesium or manganese. These elements substitute for iron in complete solid solution. A solid solution series exists between ilmenite (FeTiO3) and geikielite (MgTiO3). In this series, variable amounts of magnesium substitutes for iron in the mineral’s crystal…
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Geologic Occurrence
Most ilmenite forms during the slow cooling of magma chambers and is concentrated through the process of magmatic segregation. A large underground magma chamber can take centuries to cool. As it cools, crystals of ilmenite will begin forming at a specific temperature. These crystals are heavier than the surrounding melt and sink to the bottom of the…
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What is Ilmenite?
Ilmenite is a common accessory mineral in igneous rocks, sediments, and sedimentary rocks in many parts of the world. Apollo astronauts found abundant ilmenite in lunar rocks and the lunar regolith. Ilmenite is a black iron-titanium oxide with a chemical composition of FeTiO3. Ilmenite is the primary ore of titanium, a metal needed to make a variety of high-performance alloys. Most of the ilmenite…
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Compositional and Structural Variations
Specimens of rhodonite that contain up to 20% calcium oxide are usually grayish brown in color and are known as “bustamite.” “Fowlerite” is the name given to specimens that contain up to 7% zinc oxide. Specimens with a brown color have usually been altered by weathering. Rhodonite is one of two minerals with a chemical…
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Uses of Rhodonite
Rhodonite was once used as ore of manganese in India. Today its only uses are as lapidary materials and as mineral specimens. High-quality crystals of rhodonite can sell for very high prices. Good massive pink- to red-colored material is used as an ornamental stone or gem rough. It is typically used to make cabochons, beads, small sculptures, tumbled stones,…
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Physical Properties
Rhodonite’s diagnostic properties are its pink to red color, hardness, high specific gravity, perfect cleavage, and its close association with black manganese oxides. It is sometimes confused with rhodochrosite, which is softer and effervescent in hydrochloric acid, or thulite, which is usually not associated with black manganese oxides. The physical properties of rhodonite are summarized in the table on…
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Geologic Occurrence
Rhodonite is usually found in metamorphic rocks associated with other manganese minerals. It is also found in rocks that have been altered by contact metamorphism, hydrothermal and metasomatic processes. It is usually massive to granular in occurrence. Rarely, it is found as red triclinic crystals. Rhodonite is an uncommon mineral. It is found in a few small deposits across…
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What is Rhodonite?
Rhodonite is a pink manganese silicate mineral of variable composition that often contains significant amounts of iron, magnesium, and calcium. It has a generalized chemical composition of (Mn,Fe,Mg,Ca)SiO3. Rhodonite is often associated with black manganese oxides which may occur as dendrites, fracture-fillings, or matrix within the specimen. Other names for rhodonite include “manganese spar” and “manganolite.”
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Variscite vs. Turquoise
Variscite and turquoise are sometimes found within the same geographic area, and they also can have a similar appearance in the rough or when cut into cabochons. As a result there has been some confusion, with variscite sometimes being identified as the more common and familiar turquoise. Vendors with uncertainty have been known to use…