Tschörtnerite
Chemical formula: Ca<sub>4</sub>(K,Ca,Sr,Ba)<sub>3</sub>Cu<sup>2+</sup><sub>3</sub>Al<sub>12</sub>Si<sub>12</sub>O<sub>48</sub>(OH)<sub>8</sub>·20H<sub>2</sub>O
Tschörtnerite is a very rare, blue zeolite group mineral, forming characteristic cubic crystals.
Properties
- Mohs hardness
- 5
- Luster
- Vitreous
- Streak
- Pale blue
- Density
- 2.41
- Cleavage
- Perfect on {001}
- Fracture
- Conchoidal
- Transparency
- Transparent
- Crystal system
- Cubic
Diagnostic features
## Identification The most important diagnostic feature of tschörtnerite is its crystal habit – perfectly formed, sharp cubes of an intense blue color. The combination of this form, color, vitreous luster, and specific occurrence (Eifel volcanism) is practically unequivocal. ## Distinguishing from Similar Minerals It can be confused with haüyne, which is also blue, crystallizes in the isometric system, and occurs in the same geological environment. However, tschörtnerite usually forms sharper and more regular cubes, while haüyne more often occurs as rounded grains or rhombic dodecahedra. The presence of copper in tschörtnerite's composition is a distinguishing feature. ## Crystal Forms It crystallizes in the form of simple cubes {100}, sometimes with small faces of the rhombic dodecahedron {110}. Crystals are usually small, not exceeding 2 mm, and occur as single individuals or small groups grown on the host rock.
Geological environment
## Genesis It forms under low-temperature hydrothermal activity within altered limestone xenoliths, entrained by leucite-tephrite lava. It is a secondary mineral, crystallizing in cavities and fissures of the rock. ## Mineral Associations It most commonly co-occurs with ettringite, thaumasite, willhendersonite, as well as various hydrated calcium silicates such as afwillite and hillebrandite. ## Localities The only confirmed locality of tschörtnerite in the world is its type locality – the Bellberg volcano near Ettringen, in the Eifel region, Rhineland-Palatinate, Germany.
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued specimens are those with sharp, well-formed, intensely blue crystals, contrastingly set on a light rock matrix. The size of the crystals, their number on the specimen, and the absence of mechanical damage significantly increase the collector's value. ## Popular Localities All specimens available on the collector's market come from a single location – the Bellberg volcano in Germany. This makes tschörtnerite one of the most sought-after microminerals from this region.
Care and storage
## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Brief rinsing in distilled water is permissible, but prolonged soaking should be avoided, as zeolites can undergo alterations in contact with water. ## What to Avoid Ultrasonic cleaners, strong detergents, and acids should be absolutely avoided. The mineral is sensitive to high temperatures, which can lead to its dehydration and destruction of its structure. It should be protected from impacts and scratching. ## Storage It is recommended to store specimens in separate, padded boxes or display cases, in stable room conditions. They should be protected from direct sunlight and sudden temperature changes.