Stichtite
Chemical formula: Mg₆Cr₂(CO₃)(OH)₁₆ · 4H₂O
Stichtite is a rare mineral from the hydrotalcite group, characterized by an intense pink-purple color, often found in serpentinites.
Description
## Characteristics Stichtite is a hydrated magnesium chromium carbonate, belonging to the hydrotalcite group. It usually occurs as compact, fibrous, or platy aggregates; rarely, it forms small, hexagonal crystals. Its most recognizable feature is its intense color, ranging from pink to purple, which makes it valued by collectors. It often forms layered structures, and its surface can have a waxy luster. ## Physical Properties This mineral is characterized by a low Mohs hardness of 1.5-2, making it relatively soft. Stichtite's luster is waxy, and its streak is white to pale purple. It is transparent, and its density is approximately 2.16 g/cm³. It possesses perfect cleavage in one direction. ## Colors and Varieties Stichtite occurs in shades of pink, purple, and violet, often with an admixture of white or green when associated with serpentinite. There are no specific commercial varieties, but the intensity and uniformity of its color are important for its collector's value. ## History and Name Stichtite was discovered in 1910 in Tasmania, Australia. The mineral's name comes from Robert Carl Sticht, the director of the Mount Lyell Mining and Railway Company, where the mineral was first found. ## Uses Stichtite has no industrial applications. It is exclusively a collector's mineral, valued for its rarity and attractive color. It is sometimes cut as an ornamental stone, but due to its low hardness and perfect cleavage, it requires caution.
Diagnostic features
## Identification Stichtite can be identified by its characteristic, intense pink-purple color and waxy luster. It often occurs in association with green serpentinite, creating contrasting color combinations. Low hardness (can be scratched with a fingernail) is also a diagnostic feature. ## Distinguishing from Similar Minerals Stichtite is sometimes confused with other minerals of similar color, such as sugilite or purpurite. It differs from sugilite by its significantly lower hardness and different genesis. Purpurite has higher hardness and usually a more intense, darker purple color. Stichtite can also be confused with some varieties of serpentinite, but its distinct pink-purple color is unique. ## Crystal Forms Stichtite most commonly occurs as massive, compact, platy, or fibrous aggregates. Rarely, it forms small, hexagonal crystals, which are usually microscopic. Aggregates often exhibit a layered structure.
Geological environment
## Genesis Stichtite is a secondary mineral, formed by the hydrothermal alteration of ultramafic rocks rich in magnesium, such as serpentinites. It forms at low temperatures, in the presence of solutions containing chromium and carbonates. It often occurs in veins and fissures within serpentinites. ## Mineral Associations Stichtite most commonly co-occurs with serpentinite, chromite, brucite, and other minerals from the hydrotalcite group. It can sometimes be found in association with magnetite. ## Localities The most important and well-known localities of stichtite are in Tasmania (Australia), where it was discovered. Other occurrences include South Africa (Barberton), Canada (Quebec), USA (California), and Russia (Urals).
Rarity
Rare
Collector aspects
## Quality Criteria The most prized stichtite specimens are characterized by an intense, uniform pink-purple color. The size and purity of the aggregates are also important, as is the contrast with the surrounding host rock, often green serpentinite. Specimens with well-formed, though rare, crystals are particularly sought after. ## Popular Localities The most valued stichtite specimens come from Tasmania, Australia, where the mineral was discovered and where its most spectacular forms occur. Specimens from South Africa are also highly regarded due to their intense colors.
Care and storage
## Cleaning Stichtite is a soft mineral, so it should be cleaned very gently. It is recommended to use a soft, dry cloth or brush to remove dust. For heavier soiling, lukewarm water with a small amount of mild soap can be used, followed by thorough rinsing and drying. Avoid vigorous rubbing. ## What to Avoid The mineral is sensitive to acids, which can dissolve it. Avoid contact with chemicals, including strong detergents. Due to its low hardness, stichtite is easily scratched. Prolonged exposure to direct sunlight can cause color fading, so it is recommended to store it in a shaded place. Also, avoid sudden temperature changes. ## Storage Stichtite is best stored in a separate box lined with soft material to prevent scratching by harder minerals. An ideal location is one with a constant temperature and moderate humidity, away from direct sunlight.