Lindsleyite

Chemical formula: (Ba,Sr)(Zr₄+,Ca)(Fe₃+,Mg)₂(Ti₄+,Cr₃+,Fe₃+)₁₈O₃₈

Lindsleyite is a rare, black oxide mineral from the magnetoplumbite group, found as small, hexagonal crystals in kimberlites.

## Characteristics Lindsleyite is a complex oxide belonging to the magnetoplumbite group. It forms small, typically not exceeding 1 mm, tabular crystals with a hexagonal outline. It occurs as single, scattered crystals within the host rock. It is an opaque mineral with a black color and metallic luster. ## Physical Properties It is characterized by a relatively high hardness of 7.5 on the Mohs scale, and a significant density of approximately 4.65 g/cm³. The luster is metallic. This mineral does not exhibit cleavage, and its fracture is conchoidal. ## Colors and Varieties Lindsleyite is an idiochromatic mineral, meaning its chemical composition determines its constant, black color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral was named in honor of Donald H. Lindsley (born 1934), an American petrologist and mineralogist from Stony Brook University, State University of New York, in recognition of his contributions to the study of iron-titanium oxides. It was described and approved as a new mineral by the IMA in 1983. ## Uses Due to its extreme rarity and microscopic crystal sizes, lindsleyite has no industrial applications. It is solely an object of scientific and collecting interest for specialized micromount mineral collectors.

Properties

Mohs hardness: 7.5
Luster: Metallic
Streak: Black
Density: 4.65
Cleavage: None
Fracture: Conchoidal
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Amateur identification of lindsleyite is practically impossible. It requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) to determine its chemical composition. Visual characteristics, such as black color, metallic luster, and hexagonal crystal shape, are merely indicative. ## Distinguishing from Similar Minerals Lindsleyite is visually indistinguishable from other black, opaque minerals of the magnetoplumbite group, such as hawthorneite, yimengite, or mathiasite, with which it often co-occurs. Definitive distinction is only possible based on detailed chemical analysis. ## Crystal Forms It forms sharply defined, tabular crystals with a hexagonal outline. Crystals are usually very small, rarely exceeding 1 mm in diameter, and occur as single individuals in the rock.

Geological environment

## Genesis Lindsleyite is a primary mineral, crystallizing in ultramafic igneous rocks – kimberlites. It forms under high pressure and temperature conditions deep within the Earth's mantle. It is one of the accessory phase components in potassium-rich kimberlites. ## Mineral Associations This mineral co-occurs with other rare oxide minerals from kimberlites, including various minerals from the magnetoplumbite group (hawthorneite, mathiasite, yimengite), as well as ilmenite, rutile, perovskite, diopside, and phlogopite. ## Localities The most important and well-documented lindsleyite localities worldwide are kimberlites in South Africa, especially around Jagersfontein and Kimberley. It has also been reported in kimberlites in Yakutia, Russia.

Rarity

Very rare

For collectors

## Quality Criteria The collecting appeal of a lindsleyite specimen primarily depends on the size and degree of development of its crystals. Most valued are specimens with sharply defined, relatively large (for this mineral, i.e., close to 1 mm) hexagonal crystals, clearly embedded in a contrasting kimberlite matrix. Purity is not a criterion, as the mineral is opaque. ## Popular Localities The vast majority of collector specimens, including the type specimen, come from kimberlites in South Africa, mainly from mines in the Kimberley region.

Care and storage

## Cleaning Specimens containing lindsleyite, which are usually fragments of the host rock, can be cleaned with compressed air to remove dust. For heavier soiling, a soft brush and distilled water may be used, followed by thorough drying. Ultrasonic cleaners should be avoided. ## What to Avoid Contact with strong acids and chemicals should be avoided, as they could damage both the mineral itself and the accompanying rock matrix. Despite its high hardness, the crystals are small and brittle, so they should be protected from impacts and abrasion. ## Storage It is recommended to store specimens in stable conditions, away from dust and moisture. The best solution is sealed "micromount" boxes, which protect small crystals from mechanical damage and loss.

Sources

IMA Mineral List (CNMNC)