Strontioginorite

Chemical formula: SrCaB₁₄O₂₀(OH)₆·5H₂O

Strontiohillerite is a rare, colorless strontium and calcium borate, forming transparent, tabular crystals with perfect cleavage.

## Characteristics Strontiohillerite is a hydrated strontium and calcium borate, belonging to the hillerite group. It occurs as transparent, colorless crystals with a tabular or bladed habit, often forming radial or chaotic aggregates. Its characteristic feature is perfect cleavage in one direction, which makes specimens delicate and easily split into thin lamellae. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2-3, meaning it can be scratched with a fingernail. It has a density of 2.25 g/cm³, similar to other borates. The luster on cleavage surfaces is vitreous to pearly. It is transparent. ## Colors and Varieties Strontiohillerite is typically colorless and does not form colored varieties. It also has no trade names. ## History and Name The mineral's name refers to its chemical composition – the presence of strontium (strontio-) and its structural similarity to hillerite. It was first described in 1959 based on specimens found in the Königshall-Hindenburg mine in Reyershausen, Lower Saxony (Germany), which is its type locality. ## Applications Due to its rarity and small crystal size, strontiohillerite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or borate systematics.

Properties

Mohs hardness
2-3
Luster
Vitreous to pearly
Streak
White
Density
2.25
Cleavage
(010) perfect, (001) very good
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features of strontiohillerite include its habit (thin, tabular crystals), perfect cleavage in one direction, low hardness (2-3 on the Mohs scale), and occurrence in a specific geological environment (salt evaporites). It reacts with acids. ## Distinguishing from Similar Minerals It can be confused with other colorless borates, such as hillerite or colemanite. It differs from hillerite by the presence of strontium, which requires chemical analysis. From colemanite, it is distinguished by lower hardness and a different crystal form. Gypsum, which has even lower hardness (2), can also have a similar appearance. ## Crystal Forms It crystallizes in the monoclinic system, forming thin, tabular or bladed crystals, often elongated. These crystals arrange themselves into radial, stellate, or chaotic clusters and aggregates.

Geological environment

## Genesis Strontiohillerite is a mineral of sedimentary origin. It forms as a result of evaporation in salt basins, in rocks rich in boron, calcium, and strontium. It forms in anhydrite clays and rock salt deposits. ## Mineral Associations It most commonly co-occurs with other evaporite minerals, such as halite, sylvite, anhydrite, gypsum, colemanite, hillerite, hydroboracite, and boracite. ## Localities The most important and classic locality for this mineral is its discovery site – the Königshall-Hindenburg mine in Reyershausen, Germany. It is also known from several other localities worldwide with similar geology, including the Inder Valley in Kazakhstan and boron deposits in Death Valley, California, USA.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, transparent crystals forming aesthetic, radial aggregates. The size of the crystals and the absence of mechanical damage, which are common due to the mineral's delicacy, are important. A contrasting matrix, e.g., darker clay, enhances the visual appeal of the specimen. ## Popular Localities Specimens from the type locality in Germany (Reyershausen) have historical value. High-quality crystals also come from borate deposits in Kazakhstan and California.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to its low hardness and perfect cleavage, contact with water or other liquids is inadvisable and can lead to damage or dissolution of the mineral. ## What to Avoid Avoid contact with water, chemicals, and ultrasound. The mineral is very soft and brittle, so it must be protected from impacts, scratching, and vibrations. It should not be heated or exposed to moisture. ## Storage It is recommended to store specimens in closed, padded collector's boxes to protect them from mechanical damage, dust, and humidity changes. It is not suitable for display in open showcases.

External references

Sources

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