Macquartite

Properties

Mohs hardness

3.5

Luster

Adamantine to Resinous

Streak

Pale orange

Density

6.95

Cleavage

Perfect on {101}

Fracture

Uneven

Transparency

Transparent to Translucent

Crystal system

Monoclinic

Diagnostic features

## Identification Macquartite is primarily recognizable by its unique combination of features: intense orange-red color, occurrence as small, acicular crystals forming radial aggregates, and co-occurrence with other rare minerals from the Tiger mine. However, definitive identification requires advanced analytical methods such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Distinguishing from Similar Minerals It can be confused with other orange or red secondary lead minerals, such as wulfenite, crocoite, or vanadinite. It differs from wulfenite by its crystal habit (acicular, not tabular). From crocoite, it differs by a harder, more adamantine luster and usually smaller crystal size. Vanadinite forms hexagonal crystals, while macquartite crystallizes in the monoclinic system. However, the locality and associated minerals are key. ## Crystal Forms Crystals are most often elongated, prismatic, acicular, or bladed. They usually form radial or stellate aggregates, as well as haphazard clusters on the rock surface.

Geological environment

## Genesis Macquartite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic deposits rich in lead and copper. Its formation requires specific geochemical conditions, including the presence of chromate ions (CrO₄)²⁻, which are very rare in the natural environment. The source of chromium at the type locality (Tiger mine) was likely oxidizing primary minerals, such as vanadinite containing chromium impurities. ## Mineral Associations This mineral co-occurs with a number of other rare secondary minerals, especially from the type locality. It is most often accompanied by: dioptase, wulfenite, cerussite, chrysocolla, hematite, quartz, as well as other rare lead chromates and silicates such as phoenicochroite, hemihedrite, or wickenburgite. ## Localities The only confirmed and well-documented locality for macquartite worldwide is its discovery site – the Tiger mine in the Mammoth-Saint Anthony Mine district, Pinal County, Arizona, USA. This is a classic locality for many rare secondary minerals.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued macquartite specimens are those with well-formed, sharply terminated crystals forming aesthetic, radial aggregates. The intensity and purity of the orange-red color are crucial. Contrast with the matrix – usually whitish cerussite or quartz – is also important. Due to the microscopic nature of the mineral, the size of aggregates and individual crystals is of great significance, and specimens with crystals visible without high magnification are exceptionally desirable. ## Popular Localities The only source of collector specimens is the historic Tiger mine in Arizona, which has been inactive and inaccessible for many years. All specimens available on the market come from old collections, which further increases their value and rarity.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using compressed air to remove dust. Any contact with water or chemicals is inadvisable. Due to the microscopic size of the crystals, mechanical cleaning (e.g., with a brush) is impossible and risks damaging the specimen. ## What to Avoid Avoid contact with all liquids, including water and cleaning agents. The mineral is sensitive to acids. Protect it from high temperatures, shocks, and ultrasound. As a mineral containing lead and chromium, it requires careful handling – avoid inhaling dust and wash hands after contact. ## Storage It is recommended to store specimens exclusively in specialized micromount boxes that protect them from dust, mechanical damage, and moisture. Exposure should be away from direct sunlight and heat sources.

Sources

• IMA Mineral List (CNMNC)