Minrecordite
Chemical formula: CaZn<sup>2+</sup>(CO<sub>3</sub>)<sub>2</sub>
Minrecordite is a rare mineral of the dolomite group, being the zinc analogue of dolomite and the calcium analogue of smithsonite.
Properties
- Mohs hardness
- 3.5-4
- Luster
- Vitreous
- Streak
- White
- Density
- 3.45
- Cleavage
- Perfect on {1011}
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification Minrecordite most often forms very small, white or colorless rhombohedral crystals, often with saddle-shaped curved faces. A key diagnostic feature is its reaction with acids – it effervesces vigorously in cold, dilute hydrochloric acid. Due to the small size of the crystals, identification often requires chemical analysis (EDS) to confirm the presence of calcium and zinc. ## Distinguishing from Similar Minerals Minrecordite can be confused with other white carbonates, such as dolomite, ankerite, calcite, or smithsonite. It is distinguished from dolomite and ankerite by its vigorous reaction with cold HCl (dolomite and ankerite react weakly or not at all). Visual distinction from calcite and smithsonite is practically impossible without advanced tests confirming chemical composition (presence of both Ca and Zn). ## Crystal Forms Crystals are usually small, with a rhombohedral habit {1011}. Their saddle-shaped curvature is characteristic. It occurs as single crystals grown on a matrix, as well as in the form of fine-grained aggregates and crusts.
Geological environment
## Genesis Minrecordite is a secondary mineral, forming at low temperatures in the oxidation (weathering) zones of hydrothermal zinc and lead ore deposits, which occur in carbonate rocks (dolomites). It forms as a result of the reaction of zinc-rich solutions with surrounding dolomitic rocks. ## Mineral Associations This mineral often co-occurs with other secondary minerals of the oxidation zone. In the type locality (Tsumeb), it was found in association with duftite, calcite, malachite, and cerussite. In other localities, it may occur together with anglesite, smithsonite, hemimorphite, or hydrozincite. ## Localities The most important and type locality for minrecordite is the famous Tsumeb mine in Namibia, from which the best known specimens originate. It has also been reported in several other places around the world, including the Preguiça mine in Portugal, Lavrio in Greece, and the Kabwe (Broken Hill) mines in Zambia.
Rarity
Very rare
For collectors
## Quality Criteria The most prized minrecordite specimens are characterized by sharp, well-formed, and transparent crystals that are clearly visible on a contrasting rock matrix. Due to the mineral's rarity, even microscopic but well-formed crystals are sought after. Associations with other rare minerals, such as colorful duftite, are particularly attractive. ## Popular Localities Undoubtedly, the most known and valued source of collector specimens of minrecordite is the Tsumeb mine in Namibia. Specimens from this locality set the standard against which all others are compared. Other localities usually provide material primarily of scientific or micromount significance.
Care and storage
## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Always dry the specimen thoroughly after cleaning. ## What to Avoid Minrecordite, as a carbonate, is sensitive to acids, which cause it to effervesce vigorously. Contact with all household and laboratory chemicals should be avoided. The mineral is relatively soft and brittle, so it must be protected from impacts and scratches. ## Storage It is recommended to store minrecordite specimens in separate, padded collector boxes to prevent contact with harder minerals. It should be protected from dust and moisture.