Katophorite
Chemical formula: NaNaCa(Mg<sub>4</sub>Al)(Si<sub>7</sub>Al)O<sub>22</sub>(OH)<sub>2</sub>
Catophorite is a rare, dark green to black mineral from the amphibole group, found in metamorphic rocks and alkaline igneous rocks.
Properties
- Mohs hardness
- 5-6
- Luster
- Vitreous
- Streak
- Gray to greenish-gray
- Density
- 3.24-3.49
- Cleavage
- Perfect on {110}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Catophorite is identified by its dark color (green to black), prismatic crystal habit, and the characteristic amphibole cleavage at ~56/124°. Vitreous luster and relatively high density are also helpful features. However, definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Catophorite is difficult to distinguish from other dark amphiboles, such as hornblende, arfvedsonite, or barkevikite, without specialized testing. Hornblende typically has a more greenish-black or brownish-black color and occurs in a wider range of rocks. Arfvedsonite often exhibits stronger pleochroism in blue and green hues. Distinguishing it from other sodium-calcium amphiboles (e.g., taramite) is impossible visually. ## Crystal Forms Catophorite crystals are most often columnar or prismatic, with a hexagonal cross-section. It also occurs as granular aggregates, fibrous masses, or as embedded grains in the host rock.
Geological environment
## Genesis Catophorite is a characteristic mineral of alkaline igneous rocks, such as nepheline syenites, phonolites, and carbonatites. It also forms under high-pressure metamorphic conditions, in rocks such as glaucophane schists and eclogites, where it forms in the blueschist facies. ## Mineral Associations In igneous rocks, it co-occurs with aegirine, nepheline, albite, arfvedsonite, and eudialyte. In metamorphic rocks, its typical associated minerals include glaucophane, jadeite, epidote, garnet (almandine-pyrope), lawsonite, and titanite. ## Localities The most important catophorite localities are Langesundsfjorden in Norway (type locality), the Kola Peninsula in Russia (Khibiny and Lovozero massifs), the Ilimaussaq complex in Greenland, and Mont Saint-Hilaire in Quebec, Canada. Occurrences in metamorphic rocks are known from the Alps (Italy, Austria) and California in the USA.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are well-formed, sharply terminated, single crystals with distinct luster and an intense, dark green or black color. Specimens where catophorite contrasts with lighter background minerals (e.g., white albite or nepheline) are particularly attractive. Large, undamaged crystals are rare and command higher value. ## Popular Localities Classic and most sought-after specimens come from alkaline pegmatites of Norway (Langesundsfjorden) and from alkaline massifs on the Kola Peninsula in Russia. Specimens from Mont Saint-Hilaire in Canada are also valued for crystal quality and diversity of mineral associations.
Care and storage
## Cleaning Catophorite specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. For heavier soiling, compressed air can be used. Due to its chemical composition, contact with water and any chemical agents should be avoided. ## What to Avoid Ultrasonic cleaners should be avoided, as they can damage the specimen along cleavage planes. The mineral is sensitive to acids, which can cause etching and alter its appearance. It should be protected from prolonged exposure to moisture. ## Storage Catophorite is best stored in a dry place, in closed boxes or display cases, to protect it from dust and moisture. Due to its moderate hardness, it should be stored separately from harder minerals (e.g., quartz) to prevent scratching.