whitlockite

Chemical formula: Ca₉Mg(PO₄)₆(PO₃OH)

whitlockite

A rare calcium and magnesium phosphate, known for its occurrence in terrestrial pegmatites and as an important component of lunar rocks and meteorites.

## Characteristics Whitlockite is a mineral from the phosphate group, chemically a complex calcium and magnesium phosphate. It most often forms small, well-formed crystals with rhombohedral or tabular habits. It also occurs in granular, rosette-like aggregates and as concretions. Crystals can be transparent to translucent, with a luster ranging from vitreous to slightly resinous. ## Physical Properties The mineral's hardness is 5 on the Mohs scale, placing it in the same class as apatite. It is relatively brittle, and its density is approximately 3.12 g/cm³. It does not exhibit cleavage, and its fracture is conchoidal to uneven. It is slowly soluble in acids. ## Colors and Varieties Whitlockite is most often colorless, white, gray, or takes on delicate shades of pink and yellow. It does not form color varieties of commercial significance. Its anhydrous (hydrogen-free) counterpart, occurring in extraterrestrial environments (e.g., in meteorites), is a separate mineral called merrillite. ## History and Name The mineral was described in 1941 and named after Herbert Percy Whitlock (1868–1948), an American mineralogist and long-time curator of collections at the American Museum of Natural History in New York. The type locality is the Palermo No. 1 mine in North Groton, New Hampshire (USA). ## Uses Whitlockite has no industrial applications. However, it has great scientific significance, especially in the study of meteorites and lunar rocks, where its presence provides information about the conditions prevailing in the Solar System. It is also valued by collectors of rare minerals.

Properties

Mohs hardness
5
Color
Colourless, grey-white, light pink, light yellow; colourless in transmitted light.
Luster
Vitreous to resinous
Streak
White
Density
3.12
Cleavage
None
Fracture
Conchoidal to uneven
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Identifying features include characteristic, often rhombohedral crystals, hardness (5 on the Mohs scale), and lack of cleavage. Occurrence in paragenesis with other phosphates in granitic pegmatites is also a strong indicator. It sometimes exhibits weak, pinkish fluorescence under UV light. ## Distinguishing from Similar Minerals Whitlockite is sometimes confused with apatite, which is hexagonal and often forms prismatic crystals. It is distinguished from quartz by its significantly lower hardness (5 versus 7). Dolomite and calcite are much softer and react vigorously with hydrochloric acid, while whitlockite dissolves slowly in it. ## Crystal Forms Most commonly found are small, rhombohedral or thick tabular crystals. The mineral also forms granular aggregates, radial aggregates, and rounded nodules and concretions.

Geological environment

## Genesis Whitlockite is a secondary mineral, formed in complex granitic pegmatites, where it crystallizes in the late stages of hydrothermal processes. It is also found in sedimentary phosphorite deposits. Importantly, it is an important accessory mineral in extraterrestrial rocks – it has been identified in samples from the Moon and in many types of meteorites (chondrites, achondrites, pallasites). ## Mineral Associations In pegmatites, it coexists with other phosphates such as ludlamite, fairfieldite, triphylite, as well as with quartz, siderite, and mica. In meteorites, it is accompanied by olivine, pyroxenes, plagioclase, and troilite. ## Localities The most famous localities with well-formed crystals are mines in the USA, including the Palermo Mine in New Hampshire (type locality) and the Tip Top Mine in South Dakota. This mineral is also found in many other locations worldwide, including Australia, Germany, and Sweden, but rarely in the form of attractive specimens. Its presence has been confirmed in numerous meteorite finds globally.

Rarity

Rare

For collectors

## Quality Criteria The most highly prized whitlockite specimens are those with sharp, well-formed, and transparent crystals, set on a contrasting rock matrix. Crystal size is a key factor – specimens exceeding a few millimeters are already considered significant. Aesthetic associations with other rare phosphate minerals also add to their attractiveness. ## Popular Localities Two American localities are considered classic and provide the best whitlockite specimens in the world: the Palermo No. 1 mine in New Hampshire and the Tip Top mine in South Dakota. Specimens from these locations set the standard against which other finds are compared.

Care and storage

## Cleaning Whitlockite specimens can be safely cleaned with lukewarm water and a mild soap, using a soft brush. Ultrasonic cleaners should be avoided, as they can cause cracks in brittle crystals. ## What to Avoid As a phosphate, the mineral is sensitive to strong acids. A hardness of 5 means it can be scratched by harder minerals (e.g., quartz) or steel tools, so contact with them should be avoided. It is stable under normal lighting and temperature conditions. ## Storage It is recommended to store specimens in separate, padded boxes to protect them from scratches and mechanical damage. This applies especially to well-formed, small crystals, which are particularly delicate.

External references

Sources

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