How do I identify Alstonite?

Alstonite can be identified by its hardness of 4 - 4.5 on the Mohs scale, Colourless to snow white color. Look for these key characteristics when examining specimens.

What color is Alstonite?

Alstonite typically appears in Colourless to snow white, yellow-gray; pale gray, pale cream, pink to pale rose-red. Color can vary depending on impurities and formation conditions.

How hard is Alstonite?

Alstonite has a hardness of 4 - 4.5 on the Mohs scale. This gives it moderate hardness.

Alstonite

A variety of Minerals

What is Alstonite?

Alstonite, also known as bromlite, is a low temperature hydrothermal mineral that is a rare double carbonate of calcium and barium with the formula BaCa(CO3)2, sometimes with some strontium. Barytocalcite and paralstonite have the same formula but different structures, so these three minerals are said to be trimorphous. Alstonite is triclinic but barytocalcite is monoclinic and paralstonite is trigonal. The species was named bromlite by Thomas Thomson in 1837 after the Bromley-Hill mine, and alstonite by August Breithaupt of the Freiberg Mining Academy in 1841, after Alston, Cumbria, the base of operations of the mineral dealer from whom the first samples were obtained by Thomson in 1834. Both of these names have been in common use.

Alstonite Market Value Calculator

Estimate the market value of Alstonite using size, quality, and finish. This preview calculator is for quick context and is not a formal appraisal.

Alstonite Localities Map

See where Alstonite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.

Map preview

North ZoneCentral RidgeSouth Basin

Key Characteristics

Characteristics of Alstonite

Twinning in alstonite is ubiquitous, forming pseudohexagonal groups. The mineral has one imperfect cleavage and it breaks with an uneven fracture. It is not very hard, with a Mohs hardness of just 4 to 4 ⁄2, a little harder than fluorite, and its specific gravity is 3.70. It is soluble in dilute HCl and it is not radioactive. The trimorphs alstonite, paralstonite, and barytocalcite all have similar physical properties.

Appearance of Alstonite

Simple crystals of alstonite are not known. The crystals are invariably complex twins formed by repeated twinning, and have the form of doubly terminated pseudo-hexagonal pyramids, like those of witherite but more acute. The faces are horizontally striated perpendicular to the pseudohexagonal c crystal axis and they are divided vertically by a medial, slightly reentrant twinning line parallel to the pseudohexagonal c axis. Crystals are colourless to snow white, yellow-gray, pale gray, pale cream, pink, or pale rose-red, but the colour may fade on exposure to light. They are transparent to translucent with a white streak and vitreous lustre. The examination in polarized light of a transverse section shows that each compound crystal is built up of six differently oriented individuals arranged in twelve segments.

Composition of Alstonite

Alstonite is triclinic, but appears pseudo-orthorhombic because of twinning. The space group is P1 or P1. Alstonite appears to have a superstructure based on paralstonite without long range order of the metal cations or the CO3 groups. The structure of paralstonite is similar to that of other double carbonates.

More Images

Quick Facts

Physical Properties

Color: Colourless to snow white, yellow-gray; pale gray, pale cream, pink to pale rose-red
Hardness (Mohs): 4 - 4.5
Density: 3.67 g/cm³
Streak: White