Whewellite

Chemical formula: Ca(C₂)⁶⁺O₄·H₂O

Whewellite is a hydrated calcium oxalate, a rare organic mineral distinguished by its ability to fluoresce under ultraviolet light.

## Characteristics Whewellite is a hydrated calcium oxalate, which makes it a mineral of organic origin. It occurs as well-formed, often flattened or prismatic crystals, which can form twins. It is usually colorless, white, yellowish, or brown. Its crystals can be transparent to translucent and exhibit a vitreous luster. It is a rare mineral, sought after by collectors due to its unusual origin and properties. ## Physical Properties Whewellite is a relatively soft mineral with a hardness of 2.5-3 on the Mohs scale, meaning it can be scratched by a copper coin. Its density is approximately 2.21 g/cm³, making it a light mineral. It exhibits very good cleavage in one direction, and its fracture is conchoidal. A characteristic feature is its strong, blue-white fluorescence under shortwave UV light. ## Colors and Varieties This mineral is most often colorless or white. Yellow and brown specimens are also found. There are no named color or commercial varieties. ## History and Name Whewellite was first described in 1855. Its name honors William Whewell (1794-1866), an English polymath, philosopher of science, and mineralogist from Cambridge University. ## Uses Due to its rarity and small crystal sizes, whewellite has no industrial applications. It is solely an object of interest for collectors and scientists studying organic minerals.

Properties

Mohs hardness: 2.5-3
Luster: Vitreous
Streak: White
Density: 2.21
Cleavage: On <mi>{_101}</mi> very good; on {010}, imperfect; on {001}, {110}, indistinct.
Fracture: Conchoidal
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification A key diagnostic feature of whewellite is its strong, blue-white fluorescence under shortwave UV light. It is a relatively soft mineral (hardness 2.5-3), light, and exhibits very good cleavage. It occurs in characteristic, often twinned crystals with a vitreous luster. ## Distinguishing from Similar Minerals Whewellite can be confused with other colorless or white minerals with a vitreous luster, such as calcite, dolomite, or some zeolites. It is distinguished from calcite and dolomite by its lack of reaction with hydrochloric acid. It can be distinguished from zeolites based on crystal form and the characteristic, strong fluorescence, which most zeolites do not exhibit. ## Crystal Forms Whewellite crystals are monoclinic, often tabular, prismatic, or equant. They very often form twins, including penetration twins, which is a characteristic feature of this mineral. It also occurs as granular aggregates or radial aggregates.

Geological environment

## Genesis Whewellite is a mineral of organic origin. It forms through low-temperature hydrothermal processes, often in ore veins, marls, septaria, and coal deposits. Its formation is associated with the decomposition of organic matter, which provides oxalate ions. It can also crystallize in sedimentary environments. ## Mineral Associations It often co-occurs with calcite, barite, sphalerite, pyrite, as well as various clay minerals and bituminous substances, especially within coal deposits and argillaceous-ferruginous septaria. ## Localities Important localities worldwide include those in Germany (e.g., the lignite mine near Freital in Saxony), in the Czech Republic (around Kladno and Most), in Romania (mines in the Cavnic and Baia Sprie regions), and in Russia (Urals). It is also found in the United States.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp, and transparent crystals, especially those forming aesthetic twins. Crystals embedded in a contrasting rock matrix are also highly valued. Crystal size is significant – specimens with crystals exceeding one centimeter are rare and sought after. Color, although usually subdued, can influence attractiveness, especially in the case of specimens with a pure yellow or brown hue. ## Popular Localities Classic and most valued whewellite specimens come from historical localities in Germany (Saxony) and the Czech Republic (Kladno), where large and well-formed crystals were found in concretions and coal deposits. Specimens from Romanian mines, e.g., from Cavnic, are also popular in the collector's market.

Care and storage

## Cleaning Whewellite specimens should be cleaned very carefully due to their softness and cleavage. It is best to use a soft brush to remove dust. If washing is necessary, use distilled water and avoid strong rubbing. After cleaning, the specimen should be left to air dry completely at room temperature. ## What to Avoid Whewellite is sensitive to acids and other chemicals. Ultrasonic cleaners should be avoided, as they can damage crystals due to their cleavage. The mineral is also sensitive to high temperatures, which can lead to dehydration and structural damage. It should not be exposed to prolonged direct sunlight. ## Storage Whewellite specimens are best stored in separate, padded boxes to prevent scratching by harder minerals. They should be protected from dust, humidity, and sudden temperature changes. Display in a closed cabinet is recommended.