Paralstonite

Chemical formula: BaCa(CO₃)₂

Paralstonite is a rare barium and calcium carbonate, forming colorless or gray, dipyramidal crystals with a vitreous luster.

## Characteristics Paralstonite is a rare mineral from the carbonate group, being a double carbonate of barium and calcium. Its name refers to its structural similarity to alstonite. It typically forms small, well-developed crystals with a characteristic, dipyramidal shape, resembling two pyramids joined at their bases. Specimens are most often colorless, although they can also be smoky or pale gray. Due to its rarity and attractive crystal forms, it is a prized collector's mineral. ## Physical Properties This mineral is characterized by a hardness in the range of 4-4.5 on the Mohs scale, which places it in the group of medium-hard minerals. It has a vitreous luster, and its crystals can range from transparent to translucent. The density is approximately 3.60 g/cm³. ## Colors and Varieties Paralstonite occurs in a limited color range. Completely colorless crystals are most commonly found. Less frequently, specimens with a smoky white to light gray color are observed. There are no named color varieties or commercial varieties. ## History and Name Paralstonite was first described in 1979. Its name comes from the Greek word "pará" (παρά), meaning "beside" or "near," and the name of the mineral alstonite, reflecting its close structural and chemical similarity to that mineral. The type locality from which the first described specimens originated is the Minerva No. 1 mine in the Cave-in-Rock district in Illinois, USA. ## Uses Paralstonite has no industrial significance. Its only use is as an object of interest for mineral collectors, who value it for its rarity, aesthetic crystal forms, and origin from well-known localities.

Properties

Mohs hardness
4-4.5
Luster
Vitreous
Density
3.60
Fracture
Irregular/Uneven
Transparency
Transparent,Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Paralstonite is most easily recognized by its characteristic crystal form – sharp, hexagonal dipyramids. Auxiliary features include vitreous luster, relatively high density for a carbonate, and occurrence in association with other hydrothermal minerals such as fluorite or barite. It reacts vigorously with hydrochloric acid. ## Distinguishing from Similar Minerals Paralstonite is sometimes confused with alstonite, to which it is closely related. Distinguishing these two minerals without advanced analysis (e.g., X-ray diffraction) is practically impossible. It can also be confused with some forms of calcite or quartz; however, calcite is softer (Mohs hardness 3), and quartz is much harder (Mohs hardness 7). Witherite, another barium carbonate, usually has different crystal forms (pseudohexagonal, prismatic) and is denser. ## Crystal Forms Paralstonite crystals are typically small and take the form of sharp, steep hexagonal (or pseudohexagonal) dipyramids. It rarely forms granular or massive aggregates.

Geological environment

## Genesis Paralstonite is a hydrothermal mineral of low-temperature origin. It forms in ore veins, where it crystallizes from solutions rich in barium and calcium. Its presence is characteristic of certain fluorite-barite-zinc-lead deposits. ## Mineral Associations This mineral often co-occurs with other hydrothermal minerals. At the type locality (Cave-in-Rock), it was found in association with fluorite, calcite, barite, strontianite, benstonite, and alstonite. ## Localities The most important and well-known locality for paralstonite worldwide is its type locality – the fluorite mine complex in the Cave-in-Rock district in Hardin County, Illinois (USA). In addition, its presence has been noted in several other places around the world, including the High Pirn mine in Dumfries and Galloway, Scotland, and the zinc and lead ore deposit in Långban, Sweden.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp, and lustrous crystals of dipyramidal form. Transparent, colorless crystals are highly valued, especially those set on a contrasting matrix, such as purple fluorite. Crystal size is also an important factor – larger, undamaged specimens command higher prices. The aesthetic composition with other associated minerals is also important. ## Popular Localities By far the most desirable and classic paralstonite specimens come from its type locality – the Minerva No. 1 mine in the Cave-in-Rock district in Illinois, USA. Specimens from this locality are considered exemplary for this species and form the basis of most specialized collections.

Care and storage

## Cleaning Paralstonite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. After wet cleaning, the specimen should be thoroughly dried. ## What to Avoid As a carbonate, paralstonite is sensitive to acids, which cause it to dissolve rapidly. Contact with any household or laboratory chemicals should be avoided. The mineral is relatively soft and brittle, so it must be protected from impacts and scratching by harder minerals. ## Storage Collector's specimens of paralstonite are best stored in separate, padded boxes or display cases to prevent contact with other minerals. It can be displayed in closed cabinets, protecting it from dust and mechanical damage.

External references

Sources

Read more