Stichtite Mineral Overview
- Mineral name: Stichtite
- Mineral class: Carbonate
- Chemical formula: Mg₆Cr₂CO₃(OH)₁₆·4H₂O
- Crystal system: Trigonal
- Mohs hardness: 1.5–2
- Color range: Purple, lilac, pinkish-purple
- Luster: Waxy to earthy
- Streak: Pale lilac to white
- Cleavage: Perfect
- Fracture: Uneven to earthy
- Specific gravity: Approximately 2.0–2.2
- Transparency: Opaque to translucent
- Common locations: Australia, South Africa, Canada
- Uses: Ornamental stone, collector mineral
- Similar minerals: Sugilite, charoite, lepidolite
Physical and Optical Characteristics
Stichtite is most commonly found as massive or fibrous material, rather than as well-formed crystals. Crystals are rare and typically microscopic.
Its most distinctive feature is its vivid purple to lilac coloration, which can range from soft pastel tones to deeper magenta hues. The color is often uneven, appearing in patches or veins within host rock.
The luster is typically waxy or earthy, especially in compact masses. With a Mohs hardness of only 1.5 to 2, stichtite is very soft and can be scratched easily.
It often occurs intergrown with other minerals, particularly forming veins or patches within green serpentine, creating a strong visual contrast.
Chemical Composition and Color Origin
Stichtite is a magnesium chromium carbonate hydroxide, containing:
- Magnesium (Mg)
- Chromium (Cr)
- Carbonate groups (CO₃)
- Hydroxyl (OH) and water
The purple color is caused by the presence of chromium. Variations in chromium concentration can influence the intensity of the color.
Its structure includes a significant amount of water, contributing to its softness and relatively low density.
Formation and Geological Occurrence
Stichtite forms through alteration of chromium-rich ultramafic rocks, particularly during serpentinization processes.
Typical formation conditions include:
- Alteration of chromite-bearing rocks
- Interaction of fluids with magnesium-rich minerals
- Low-temperature hydrothermal processes
It is most commonly found:
- As veins or masses within serpentine
- In association with chromium-rich environments
Associated minerals include:
- Serpentine
- Chromite
- Magnesite
These associations reflect ultramafic rock environments.
Common Locations
Stichtite is relatively rare and found in specific localities:
- Australia (Tasmania): Dundas region (type locality and best-known source)
- South Africa: Chromium-rich deposits
- Canada: Occurrences in ultramafic terrains
Tasmanian material is especially well known for its bright color and association with serpentine.
Uses and Practical Significance
Stichtite is primarily used as an ornamental stone:
- Cabochons and beads for jewelry
- Carvings and decorative objects
- Often sold in combination with serpentine (known as “Atlantisite”)
Its softness limits its use in jewelry exposed to heavy wear.
Similar and Related Minerals
Stichtite can resemble other purple minerals:
- Sugilite: Typically harder and more uniform in color
- Charoite: Fibrous texture and more complex patterns
- Lepidolite: Micaceous and flaky rather than massive
The association with green serpentine is a key identifying feature.
Identification Notes for Collectors
- Look for purple to lilac material in veins within green serpentine
- Note very soft hardness (scratches easily)
- Observe waxy to earthy luster
- Check for association with chromium-rich rocks
- Confirm identity when distinguishing from harder purple minerals
Stichtite is a soft, chromium-bearing carbonate mineral, recognized for its distinctive purple color and occurrence in serpentine-rich environments, and is primarily valued as an ornamental and collector material.