Amicite
Chemical formula: K<sub>2</sub>Na<sub>2</sub>(Si<sub>4</sub>Al<sub>4</sub>O<sub>16</sub>)·5H<sub>2</sub>O
Amicite is a rare zeolite group mineral, forming colorless or white, pseudo-tetragonal crystals in cavities of volcanic rocks.
Properties
- Mohs hardness
- 5.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.11-2.14
- Cleavage
- Good on {100} and {010}
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The most important diagnostic feature of amicite is its characteristic crystal habit – twinned crystals forming shapes resembling tetragonal prisms and bipyramids. Other helpful features include vitreous luster, low hardness and density, and a specific occurrence environment (cavities in volcanic rocks). ## Distinguishing from similar minerals Amicite is sometimes confused with other white zeolites, such as phillipsite, thomsonite, or gismondine, with which it often co-occurs. Phillipsite usually forms more complex, cross-penetration twins. Gismondine crystallizes in pseudo-octahedral forms. Definitive differentiation of these minerals often requires advanced research methods, e.g., X-ray diffraction (XRD). ## Crystal forms Amicite crystallizes in the monoclinic system, but almost always occurs in the form of penetration twins, which give it pseudo-tetragonal symmetry. It forms simple, prismatic crystals or more complex forms resembling tetragonal bipyramids. It usually occurs as small crystal druses.
Geological environment
## Genesis Amicite is a low-temperature hydrothermal mineral. It forms in gas vesicles and cavities within alkaline volcanic rocks, such as melilite-nepheline basalts. ## Mineral associations This mineral often co-occurs with other zeolites and minerals from hydrothermal environments. Its most common associations include: calcite, aragonite, phillipsite, thomsonite, analcime, and natrolite. ## Localities The most important and classic locality for amicite, which is also its type locality, is the Höwenegg quarry in the Hegau region of Germany. Significant specimens also come from the Khibiny and Lovozero alkaline massifs on the Kola Peninsula in Russia. Occurrences have also been reported on Vinařická hora mountain in the Czech Republic.
Rarity
Very rare
For collectors
## Quality criteria The collector's value of amicite primarily depends on the quality of crystal development. The most prized specimens are those with sharp, well-formed, transparent, and lustrous crystals, forming characteristic pseudo-tetragonal shapes. The size of the crystals and the aesthetic placement of the druse on the rock matrix also significantly increase the attractiveness of the specimen. ## Popular localities The best specimens in the world are considered to be those from the type locality in Höwenegg, Germany. Rich druses from the Russian Khibiny and Lovozero massifs, where amicite forms larger aggregates, are also highly valued.
Care and storage
## Cleaning Amicite specimens should be cleaned very carefully, using a soft brush and distilled water. Avoid strong water jets, which could damage the delicate crystals. Ultrasonic cleaners are not recommended. ## What to avoid As a zeolite, amicite contains water molecules in its structure. Heating can lead to dehydration, and consequently to dulling and destruction of the crystals. It should be protected from high temperatures, direct sunlight, and contact with acids and other chemicals. Due to its relatively low hardness, it is susceptible to scratches. ## Storage Collector's specimens of amicite are best stored in separate, sealed boxes to protect them from dust and mechanical damage. Avoid keeping it in contact with harder minerals.