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Pink Cobaltoan Calcite on Matrix refers to specimens where the distinctive pink to reddish-pink cobaltoan calcite crystals are still attached to their host rock (matrix). The matrix can vary widely, often consisting of other minerals such as quartz, dolomite, or various sulfide minerals. The cobaltoan calcite itself is a variety of calcite, a common carbonate mineral, distinguished by its vibrant pink coloration caused by trace amounts of cobalt. It typically forms in botryoidal, mammillary, or rhombohedral crystal habits, often displaying excellent crystallization.
How to Identify
- Color
- Varies from pale pink to vibrant rose-pink, magenta, or reddish-pink. The color is uniform within individual crystals or masses.
- Luster
- Vitreous (glassy) to sub-vitreous, sometimes pearly on cleavage surfaces.
- Texture
- Can be granular, massive, botryoidal (grape-like), mammillary (breast-like), or in distinct rhombohedral crystals. On matrix, it often forms crusts or druzy coatings.
- Crystal Form
- Typically rhombohedral, scalenohedral, or prismatic. Often found as aggregates of small crystals, botryoidal masses, or drusy coatings on matrix.
- Cleavage
- Perfect rhombohedral cleavage in three directions, producing characteristic rhomb-shaped fragments.
- Geological Environment
- Found in hydrothermal veins, especially those associated with cobalt-nickel-silver deposits, and in the oxidized zones of polymetallic ore bodies. It often occurs with other cobalt-bearing minerals, various sulfides, quartz, and other carbonates.
Key Facts
- Hardness: 3 on the Mohs scale
- Specific Gravity: 2.71 g/cm3 (pure calcite, cobalt substitution slightly increases it)
- Crystal System: Trigonal
- Color: Pink, rose-pink, magenta, reddish-pink
- Luster: Vitreous to sub-vitreous, sometimes pearly
- Transparency: Transparent to translucent
- Fracture: Conchoidal to uneven
- Cleavage: Perfect rhombohedral in three directions at 74°55'
- Composition: Calcium carbonate (CaCO3) with significant substitution of cobalt (Co2+) for calcium (Ca2+)
Quick Check
- Color: Pink to reddish-pink
- Luster: Vitreous to sub-vitreous
- Streak: White
Physical Characteristics
- Crystal Habit: Rhombohedral, scalenohedral, prismatic, massive, granular, botryoidal, mammillary, stalactitic, fibrous, lamellar.
- Cleavage Type: Perfect rhombohedral {1011}
- Fracture Type: Conchoidal to uneven
- Tenacity: Brittle
- Luster Type: Vitreous to sub-vitreous, sometimes pearly on cleavage surfaces
Formation
Cobaltoan calcite forms as a secondary mineral in the oxidized zones of cobalt-bearing ore deposits, or in hydrothermal veins where cobalt-rich fluids interact with carbonate rocks or pre-existing calcite. The pink to red color is due to the substitution of cobalt (Co2+) for calcium (Ca2+) in the calcite (CaCO3) crystal lattice. The intensity of the pink color is directly proportional to the concentration of cobalt.
Usage
Primarily a collector's mineral due to its aesthetic appeal. It has no significant industrial or commercial uses beyond its value as a specimen.
Age Distribution
Forms in various geological ages, typically associated with hydrothermal activity and polymetallic ore deposits.
Where to Find
Bou Azzer, Anti-Atlas Mountains, Morocco
World-renowned for producing some of the finest and most intensely colored pink cobaltoan calcite specimens, often associated with erythrite and other cobalt minerals.
Katanga Copperbelt, Democratic Republic of Congo
Known for significant deposits of cobalt, producing cobaltoan calcite, though often less vibrant than Moroccan material.
Tsumeb Mine, Namibia
Historically famous for a wide array of rare minerals, including cobaltoan calcite, often in association with other secondary minerals.
Alston Moor, Cumbria, England
Occurrences of cobaltoan calcite have been noted in some of the historic lead-zinc mining districts.
Finding Tips
Look for Cobalt-Rich Environments
Focus exploration in areas known for cobalt-nickel-silver mineralization or polymetallic sulfide deposits, particularly in their oxidized zones or associated hydrothermal veins.
Identify Associated Minerals
Cobaltoan calcite often co-occurs with other cobalt minerals (e.g., erythrite), various sulfide minerals (e.g., chalcopyrite, pyrite), quartz, and other carbonates. The presence of these minerals can indicate a favorable environment.
Observe Color and Crystal Habit
The distinctive pink to reddish-pink color and typical calcite crystal habits (rhombohedral, botryoidal) are key visual identifiers. Look for these characteristics on exposed rock surfaces or in mine dumps.
Test for Effervescence
Like all calcite, cobaltoan calcite will effervesce (fizz) vigorously when a drop of dilute hydrochloric acid (HCl) is applied to its surface. This helps distinguish it from similar-looking silicates or other non-carbonate minerals.
Similar Rocks
Rhodochrosite
MnCO3
Also known as: Manganese Spar
Manganoan Calcite
CaCO3 (with Mn2+ substitution)
Also known as: Manganocalcite
Erythrite
Co3(AsO4)2·8H2O
Also known as: Cobalt Bloom
Scientific Classification
- Mineral Class
- Carbonates
- Group
- Calcite Group
- Crystal System
- Trigonal
- Chemical Formula
- CaCO3 (with Co2+ substitution)
- Composition
- Calcium carbonate with varying amounts of cobalt. The cobalt content can range from trace amounts to several weight percent, directly influencing the intensity of the pink color.
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