Jonesite

Chemical formula: KBa₂Ti⁴⁺₂(Si₅Al)O₁₈·nH₂O

Jonesite is a very rare silicate mineral, forming colorless, bladed crystals, discovered in mines in California.

## Characteristics Jonesite is a hydrated potassium, barium, titanium, and aluminum silicate. It occurs as very small, colorless, bladed or fibrous crystals, which typically form radial aggregates or chaotic clusters. Individual crystals are elongated and flattened, reaching up to 1 mm in length, although they are most often much smaller. Due to its size and appearance, it is a mineral of interest mainly to micromineral collectors. ## Physical Properties Jonesite crystals exhibit perfect cleavage in one direction, which accounts for their tendency to form thin, bladed shapes. The mineral has a vitreous luster. Its Mohs hardness is 3-4, and its density is approximately 3.16 g/cm³. ## Colors and Varieties Jonesite is colorless and does not form colored varieties. ## History and Name The mineral was discovered in 1974 in samples from the California State Gem Mine in San Benito County and the Dallas Gem Mine in San Benito County, California, USA. It was named after Francis T. Jones (1905-1993), an American microscopist and micromineral collector, who first observed this mineral. ## Uses Jonesite has no industrial application and is solely an object of collector interest, especially among specialists in rare minerals and micromounts.

Properties

Mohs hardness: 3-4
Color: Colorless
Luster: Vitreous
Streak: White
Density: 3.25
Cleavage: {010}
Fracture: Irregular/Uneven
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Jonesite is recognized by its characteristic form – colorless, bladed crystals forming radial aggregates. It occurs in a very specific geological environment, in association with other rare minerals. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other fibrous or bladed silicates occurring in the same environment, such as neptunite or joaquinite, but differs from them by its lack of color. Unlike many zeolites, it forms more defined, bladed crystals. ## Crystal Forms It forms elongated, flattened crystals with a bladed cross-section. These crystals often arrange themselves into radial or stellate aggregates, as well as disordered, tangled clusters.

Geological environment

## Genesis Jonesite forms as a result of hydrothermal processes in natrolite veins cutting serpentinites. It is a secondary mineral, crystallizing at low temperatures from solutions rich in barium, titanium, and silica. ## Mineral Associations This mineral co-occurs with natrolite, joaquinite-(Ce), neptunite, diopside, bementite, leucosphenite, and serpentine. ## Localities Jonesite is known exclusively from a few localities in San Benito County, California, USA. The main localities are the type localities: the California State Gem Mine (also known as the Dallas Gem Mine) and the Numero Uno Mine.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens are those with well-formed, distinct radial aggregates of colorless crystals, contrasting with the darker matrix rock. The absence of damage to the delicate needles and blades is important. Due to the microscopic nature of the mineral, the aesthetics of the entire cluster are key. ## Popular Localities The only source of jonesite specimens is the mines in the New Idria area, San Benito County, California. Specimens from these historic localities are highly sought after by collectors specializing in rare minerals and micromounts.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Due to the delicate nature of the crystals, contact with water and brushes that could damage them should be avoided. ## What to Avoid All chemicals, ultrasonics, and sudden temperature changes should be avoided. The crystals are brittle and susceptible to mechanical damage. ## Storage It is recommended to store specimens in specialized micromount boxes that protect them from dust, shocks, and mechanical damage. Exposure to moisture should be avoided.