Redledgeite

Chemical formula: Ba(Ti<sup>4+</sup><sub>6</sub>Cr<sup>3+</sup><sub>2</sub>)O<sub>16</sub>

Redledgeite is a very rare oxide mineral from the hollandite group, forming microscopic, prismatic crystals of an intensely red color.

## Characteristics Redledgeite is an extremely rare barium, titanium, and chromium oxide, belonging to the hollandite group. It occurs as very small, elongated, prismatic crystals, rarely exceeding 1 mm in length. Its most distinctive feature is its intense, ruby-red color. The crystals exhibit strong dichroism – their color changes depending on the observation direction, from red to yellowish-brown. Due to its extreme rarity and microscopic size, it is a mineral known primarily within specialized collector and scientific circles. ## Physical Properties The crystals have a luster described as submetallic to adamantine. Hardness on the Mohs scale is estimated at 6-7. The mineral is opaque, only translucent on thin edges. It is brittle and exhibits an uneven fracture. ## Colors and Varieties The dominant and only known color of redledgeite is deep red, often described as ruby-red. No varieties of this mineral are distinguished. ## History and Name The mineral was discovered in the Red Ledge Mine in Nevada County, California (USA), from which it derives its name. It was described in 1962 by Joseph Murdoch and Joseph S. Doughty. The type locality is the only confirmed occurrence of this mineral in the world. ## Applications Redledgeite has no industrial applications. Its significance is purely scientific and collectible, as a unique member of the hollandite group.

Properties

Mohs hardness
6-7
Luster
Sub-Adamantine
Streak
Brownish-yellow
Density
4.98
Cleavage
Good on {110}
Fracture
Uneven
Transparency
Translucent to Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Identification of redledgeite is based on its unique characteristics: intense ruby-red color, prismatic crystal habit, high luster, and occurrence in a specific geological environment. The presence of chromium, titanium, and barium in chemical analysis is also crucial. Due to its size, positive identification requires the use of a microscope and advanced analytical techniques (e.g., EDS). ## Distinguishing from Similar Minerals It can be confused with other red microscopic minerals, such as cinnabar or realgar, but redledgeite is distinguished by significantly greater hardness and a different crystal habit. From other minerals of the hollandite group, it is distinguished by the dominance of chromium and barium in its composition and its characteristic red color. ## Crystal Forms It forms elongated, slender crystals with a prismatic habit, often terminated by a pyramid. Crystals are usually striated along the main axis. They occur as single, isolated needles or small, radial aggregates growing on the host rock.

Geological environment

## Genesis Redledgeite forms under specific conditions within metamorphosed ultramafic rocks (serpentinites) rich in chromium. Its crystallization is associated with low-temperature hydrothermal processes that led to the mobilization and concentration of barium, titanium, and chromium. In the type locality, it occurs in baryte veins cutting chromitite. ## Mineral Associations This mineral co-occurs with baryte, chromite, chromian muscovite (fuchsite), pyrite, quartz, joaquinite-(Ce), and benitoite. ## Localities The only confirmed and described occurrence of redledgeite in the world is its type locality – the Red Ledge Mine in the Washington District, Nevada County, California, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly prized redledgeite specimens are those with well-formed, sharply terminated crystals of intense, ruby-red color and strong luster. Contrast with a light host rock (most often baryte) is important, as it highlights the red needles. Crystal size is key – any specimen with crystals exceeding 1 mm is considered exceptional. The aesthetic arrangement of crystals on the matrix also significantly increases the specimen's value. ## Popular Localities All collectible specimens come from a single location in the world: the Red Ledge Mine in California, USA. This mine has long been inactive and inaccessible, meaning new specimens do not appear on the market, and historical collections are extremely sought after.

Care and storage

## Cleaning Redledgeite specimens are typically microscopic and embedded in the host rock. Self-cleaning is not recommended to avoid damaging the brittle crystals. If absolutely necessary, compressed air can be used to remove dust. ## What to Avoid Avoid contact with chemicals, acids, and ultrasonic cleaners, which can destroy delicate crystals. Do not expose the specimen to sudden temperature changes. ## Storage Specimens should be stored in stable conditions, away from dust and vibrations. The best solution is a sealed "micromount" box, which protects the mineral and allows for safe observation under a microscope.

Sources

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