Carmichaelite

Chemical formula: (Ti⁴⁺,Cr³⁺,Fe³⁺)(O,OH)₂

Carmichaelite is a rare titanium, chromium, and iron oxide, occurring as tiny, cinnamon-brown crystals.

## Characteristics Carmichaelite is a very rare mineral from the oxide group. It forms small, tabular or prismatic crystals, usually not exceeding 1 mm in size. Its most characteristic visual features are its cinnamon-brown color and metallic luster. ## Physical Properties This mineral is characterized by a hardness of 6 on the Mohs scale. It has a metallic luster and is translucent. Due to its extreme rarity and small crystal size, many of its physical properties, such as density, have not been thoroughly investigated. ## Colors and Varieties Carmichaelite occurs in a uniform, cinnamon-brown color. No color or commercial varieties have been distinguished. ## History and Name The mineral's name comes from Ian Carmichael (1930-2011), a professor of petrology at the University of California, Berkeley, in recognition of his contributions to the study of minerals and volcanic rocks. Carmichaelite was approved as a new mineral by the International Mineralogical Association (IMA) in 1998. ## Uses Due to its extreme rarity and microscopic size, carmichaelite has no industrial applications. It is of purely scientific significance and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
6
Luster
Metallic
Density
0
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of carmichaelite is possible almost exclusively in laboratory conditions using advanced techniques such as X-ray microanalysis (EDS/WDS). In collecting conditions, identification relies on knowledge of the locality, host rock (kimberlite), and co-occurring minerals. Observation under a microscope may reveal characteristic, tiny, cinnamon-brown crystals. ## Distinguishing from Similar Minerals It can be confused with other small, brown accessory minerals in kimberlites, such as perovskite or some garnets. Definitive differentiation requires chemical composition analysis, confirming the dominance of titanium, chromium, and iron. ## Crystal Forms Carmichaelite forms very small, individual crystals with a tabular or short-prismatic habit, up to 1 mm in size.

Geological environment

## Genesis Carmichaelite is a mineral of magmatic origin. It forms in ultrabasic volcanic rocks, such as kimberlites. It crystallizes as an accessory mineral in the late stages of these rocks' formation. ## Mineral Associations This mineral occurs in association with other minerals typical of kimberlites, such as diopside, phlogopite, ilmenite, perovskite, pyrope, and serpentine. ## Localities The only confirmed and described occurrence of carmichaelite in the world is its type locality - Garnet Ridge in Apache County, Arizona, USA. This is an area where kimberlite pipes occur.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a carmichaelite specimen is determined by the size and degree of development of its microscopic crystals, as well as their quantity on the rock matrix. The most desirable specimens are those where the crystals are clearly visible, undamaged, and contrast with the surrounding rock. Precise labeling and confirmation of the mineral's identification are also crucial. ## Popular Localities The only source of carmichaelite specimens is its type locality at Garnet Ridge in Arizona, USA. All materials available on the collector's market originate from this single location.

Care and storage

## Cleaning Due to their microscopic size and embedding in the host rock, carmichaelite specimens generally do not require and should not be cleaned. Any attempt at mechanical cleaning risks irreversible damage or loss of the crystals. ## What to Avoid Contact with chemicals, ultrasound, and any cleaning tools should be avoided. Specimens should be protected from dust and shocks. ## Storage It is recommended to store specimens in specialized "micromount" boxes, which protect them from mechanical damage and dust, while allowing observation under a microscope.

External references

Sources

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