Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Cobaltocalcite is a striking pink to reddish-pink variety of the common mineral calcite. Its vibrant color is due to the presence of cobalt substituting for calcium in its chemical structure. It shares all the fundamental physical and chemical properties of calcite, including its characteristic rhombohedral cleavage and effervescence in acid, but is distinguished by its distinct coloration. It often forms in botryoidal, mammillary, or stalactitic habits, as well as in typical calcite crystal forms.
How to Identify
- Color
- Ranges from pale pink to vibrant rose-pink, often with a reddish tint. The intensity of the color is directly related to the concentration of cobalt.
- Luster
- Vitreous to sub-vitreous, sometimes pearly on cleavage surfaces.
- Texture
- Can be massive, granular, botryoidal, mammillary, stalactitic, or in well-formed rhombohedral crystals.
- Crystal Form
- Typically rhombohedral, scalenohedral, prismatic, or tabular. Often found in aggregates or crusts.
- Cleavage
- Perfect rhombohedral cleavage in three directions, producing characteristic rhomb-shaped fragments.
- Geological Environment
- Found in the oxidation zones of cobalt-rich hydrothermal ore deposits, often associated with other secondary cobalt minerals (e.g., erythrite), copper minerals, and sometimes nickel minerals. Also occurs in some low-temperature hydrothermal veins.
Key Facts
- Hardness: 3 on the Mohs scale
- Specific Gravity: 2.71 g/cm³ (similar to pure calcite, Co substitution has minor effect)
- Crystal System: Trigonal
- Color: Pink, rose-pink, 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 cobalt (Co) substitution for calcium.
Quick Check
- Color: Pink to reddish-pink
- Luster: Vitreous
- Streak: White
Physical Characteristics
- Crystal Habit: Rhombohedral, scalenohedral, prismatic, tabular; also massive, granular, botryoidal, mammillary, stalactitic, encrusting.
- Cleavage Type: Perfect rhombohedral {1011}
- Fracture Type: Conchoidal to uneven
- Tenacity: Brittle
- Luster Type: Vitreous to sub-vitreous, pearly on cleavage surfaces
Formation
Cobaltocalcite is a variety of calcite (CaCO3) where a significant portion of the calcium (Ca) ions are substituted by cobalt (Co) ions within the crystal lattice. This substitution gives the mineral its characteristic pink to reddish-pink color. It typically forms in the oxidation zones of cobalt-bearing sulfide deposits, often in association with other cobalt, copper, and nickel minerals. It can also form in hydrothermal veins.
Usage
Primarily a collector's mineral due to its attractive color. It is not a primary ore for cobalt, but its presence can indicate the proximity of cobalt mineralization. Historically, some pink calcites might have been used as ornamental stones, but its relative rarity and softness limit widespread industrial applications.
Age Distribution
Forms in various geological ages, typically associated with hydrothermal alteration and oxidation zones of cobalt-rich ore deposits.
Where to Find
Katanga Province, Democratic Republic of Congo
World-renowned for producing some of the finest and most intensely colored Cobaltocalcite specimens, often in botryoidal or mammillary forms.
Bou Azzer, Anti-Atlas Mountains, Morocco
Another significant locality, known for producing excellent pink Cobaltocalcite crystals and aggregates, often associated with cobalt arsenides.
Tsumeb Mine, Namibia
Historically produced beautiful specimens, though less common than from Congo or Morocco.
Alston Moor, Cumbria, England
Known for some occurrences, though typically less vibrant than African material.
Various localities in the United States
Minor occurrences have been reported in states like Missouri and Arizona, often in association with lead-zinc-copper deposits.
Finding Tips
Look for Cobalt-Rich Deposits
Focus your search on areas known for cobalt mineralization, particularly the oxidized zones of sulfide deposits. The presence of other secondary cobalt minerals like erythrite (cobalt bloom) can be a good indicator.
Examine Hydrothermal Veins
Cobaltocalcite can form in low-temperature hydrothermal veins, so investigate such geological structures in mineralized areas.
Check for Associated Minerals
It often occurs with other carbonates, quartz, barite, and various cobalt, copper, and nickel minerals. Identifying these associated minerals can help pinpoint potential Cobaltocalcite occurrences.
Test for Effervescence
Like all calcites, Cobaltocalcite will effervesce (fizz) vigorously when a drop of dilute hydrochloric acid is applied to its surface. This is a key diagnostic test.
Observe Color and Habit
The distinctive pink to reddish-pink color and common botryoidal or rhombohedral habits are strong indicators.
Similar Rocks
Calcite
CaCO3
Also known as: Calcium Carbonate
Rhodochrosite
MnCO3
Also known as: Manganese Carbonate
Dolomite
CaMg(CO3)2
Also known as: Calcium Magnesium Carbonate
Sphaerocobaltite
CoCO3
Also known as: Cobalt Carbonate
Scientific Classification
- Mineral Class
- Carbonates
- Group
- Calcite Group
- Crystal System
- Trigonal
- Chemical Formula
- CaCO3 (with Co substitution)
- Composition
- Calcium carbonate with varying amounts of cobalt. The cobalt content can range from trace amounts to several weight percent, directly influencing the color intensity. Minor amounts of magnesium, iron, or manganese may also be present.
Explore Cobaltocalcite
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.