Celsian
Chemical formula: BaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>
Celsian is a rare barium feldspar, distinguished by its high density and occurrence as colorless, white, or yellowish crystals.
Properties
- Mohs hardness
- 6-6.5
- Luster
- Vitreous to pearly
- Streak
- White
- Density
- 3.31-3.4
- Cleavage
- Perfect on {001}, Good on {010}
- Fracture
- Conchoidal to uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The most important diagnostic feature of celsian, distinguishing it from other feldspars, is its high specific gravity (approximately 3.3-3.4 g/cm³). This can be estimated by comparing the weight of a specimen with a potassium or sodium feldspar of similar size — celsian will feel noticeably heavier. The presence of perfect cleavage in two directions is typical for feldspars. ## Distinguishing from Similar Minerals - **Other feldspars (orthoclase, albite, anorthite)**: are significantly lighter (density approx. 2.5-2.8 g/cm³). - **Baryte**: has a similarly high density but is much softer (hardness 3-3.5) and has a different crystal habit. - **Quartz**: is slightly harder (hardness 7) and does not exhibit cleavage, having a conchoidal fracture. ## Crystal Forms Celsian forms tabular and short-prismatic crystals, often with a complex structure resulting from numerous twinning (Carlsbad, Baveno, Manebach). It also occurs in granular and massive aggregates.
Geological environment
## Genesis Celsian is a characteristic mineral of barium- and manganese-rich metamorphic rocks. It forms under conditions of contact and regional metamorphism, often within manganese deposits. It is found in skarns, gneisses, and also in some dolomites. It occurs less frequently in igneous rocks, such as nepheline syenites. ## Mineral Associations This mineral often co-occurs with other barium and manganese minerals, such as baryte, cymrite, hausmannite, jacobsite, as well as with hyalophane, rhodochrosite, rhodonite, and quartz. ## Localities The most important celsian localities worldwide are: - Jakobsberg mine, Värmland, Sweden (type locality). - Broken Hill, New South Wales, Australia - known for large, well-formed crystals. - Benallt mine, Gwynedd, Wales, UK - source of classic, twinned crystals. - Franklin and Sterling Hill, New Jersey, USA - occurs in zinc-manganese deposits. - Otjosondu, Namibia.
Rarity
Rare
For collectors
## Quality Criteria Well-formed, sharp crystals with distinct luster and good transparency are most valued by collectors. Specimens exhibiting classic feldspar twinning (e.g., Baveno twins) are particularly sought after. The value of a specimen is also enhanced by its association with other rare minerals, such as cymrite or taramellite. ## Popular Localities Specimens from historical localities such as Jakobsberg in Sweden and Broken Hill in Australia are considered classic and most desirable. Well-formed crystals from the Benallt mine in Wales are also highly prized.
Care and storage
## Cleaning Celsian specimens should be cleaned gently, using a soft brush and distilled water. For heavier soiling, a mild soap solution can be used, followed by thorough rinsing and drying of the specimen. ## What to Avoid The mineral is sensitive to sudden temperature changes. Avoid cleaning in ultrasonic cleaners, which can cause fracturing along cleavage planes. Also, avoid contact with strong acids and bases. ## Storage Celsian, with a hardness of 6-6.5, is relatively scratch-resistant but should be stored separately from harder minerals such as quartz or corundum. Due to its cleavage, specimens should be protected from impacts and falls. It is best to store them in individual, padded boxes.