Caoxite
Chemical formula: Ca(C<sub>2</sub>)<sup>6+</sup>O<sub>4</sub>·3H<sub>2</sub>O
Caoxite is an organic mineral (calcium oxalate), found in bottom sediments and septarian concretions, characterized by its straw-yellow color and fibrous appearance.
Properties
- Mohs hardness
- 2.5-3
- Luster
- Vitreous, Pearly
- Streak
- White
- Density
- 2.22
- Cleavage
- Perfect on {100}, good on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Caoxite can be identified by its characteristic fibrous or acicular crystals, often forming radial aggregates. Its straw-yellow color, vitreous luster, and occurrence in voids of sedimentary rocks (e.g., septaria) are key features. It is soft and brittle. ## Distinguishing from Similar Minerals It can be confused with other oxalate minerals, such as whewellite or weddellite, from which differentiation requires advanced research methods (e.g., XRD). From zeolites (e.g., natrolite) with a similar appearance, it is distinguished by lower hardness and genesis. Unlike many zeolites, caoxite does not effervesce in contact with hydrochloric acid but undergoes slow decomposition. ## Crystal Forms It forms elongated, prismatic, or acicular crystals. It is most commonly found in the form of radial or fibrous aggregates, as well as spherulites and rosettes filling small fissures and rock cavities.
Geological environment
## Genesis Caoxite is a mineral of organic origin, formed during the diagenesis of organic matter in a sedimentary environment. It forms at low temperatures under anaerobic conditions. Its formation is associated with the decomposition of plant or animal remains in the presence of calcium ions. ## Mineral Associations It most commonly co-occurs with calcite, siderite, pyrite, marcasite, whewellite, weddellite, and clay minerals. It is found in siderite concretions and argillaceous septaria. ## Localities The most important and classic occurrences of this mineral are in the Czech Republic, in the Louny region (Černčice, Vršovice), where it was discovered. It has also been reported in Baltic Sea sediments and in lake sediments in Switzerland (Lake Zurich).
Rarity
Very rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, distinct radial aggregates of an intense, straw-yellow color. Contrast with the dark host rock (most often siderite or claystone) is important. The size of the aggregates and the absence of damage to the delicate crystal needles significantly increase the specimen's value. ## Popular Localities By far the most sought-after and classic specimens come from the Czech Republic, from the type locality in the vicinity of Černčice and Vršovice. These are considered exemplary for this mineral.
Care and storage
## Cleaning Caoxite specimens should be cleaned very carefully, using a soft brush to remove dust. Brief rinsing in distilled water is permissible, followed by thorough drying. Ultrasonic cleaners should be avoided, as they can damage delicate crystals. ## What to Avoid The mineral is sensitive to acids, which cause its decomposition. It should be protected from prolonged exposure to moisture and high temperatures, which can lead to dehydration and destruction of the crystal structure. It should not be exposed to direct sunlight. ## Storage Collectible caoxite specimens are best stored in closed, dry containers or display cases, away from heat and light sources. Due to its brittleness and low hardness, it should be stored separately to avoid scratches from harder minerals.