Spurrite
Chemical formula: Ca<sub>5</sub>(SiO<sub>4</sub>)<sub>2</sub>(CO<sub>3</sub>)
Spurrite is a rare calcium carbonate-silicate, forming granular aggregates in contact metamorphic zones of carbonate rocks.
Properties
- Mohs hardness
- 5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.01
- Cleavage
- Good on {001}
- Fracture
- Uneven, Conchoidal
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Spurrite is most easily identified by its occurrence in characteristic, granular or fibrous aggregates in contact metamorphic rocks. Reaction with dilute hydrochloric acid (effervescence) is a diagnostic feature, but it should be performed carefully on an inconspicuous part of the specimen. A pale blue or lilac hue can also be helpful in identification. ## Distinguishing from Similar Minerals It can be confused with other skarn minerals, such as wollastonite or some zeolites. Wollastonite does not react with hydrochloric acid. It is distinguished from zeolites by its higher hardness and density. In rare cases, when it forms purple crystals, it may resemble some varieties of quartz, but it is much softer than quartz. ## Crystal Forms Well-developed crystals are rare and usually appear as small, tabular or short, prismatic forms, often with oblique terminations. It typically forms compact, granular, fibrous, or radial aggregates.
Geological environment
## Genesis Spurrite is a mineral typical of high-grade contact metamorphism environments. It forms as a result of the interaction of hot silicate magma with carbonate rocks, such as limestones and marbles. This process occurs under conditions of high temperature and relatively low pressure, in the direct contact zone of a magmatic intrusion with sedimentary rock. ## Mineral Associations It often coexists with other minerals characteristic of skarns and the sanidinite facies, such as larnite, merwinite, gehlenite, vesuvianite, grossular (garnet), wollastonite, calcite, and brucite. ## Localities Important localities worldwide include Terneras in Durango and Velardeña in Mexico; Riverside County in California and the Tres Piedras area in New Mexico (USA); Scawt Hill in Northern Ireland; Fuka in Japan; and the Hatrurim Formation in Israel.
Rarity
Rare
For collectors
## Quality Criteria The most sought-after specimens by collectors are those with well-formed, transparent crystals, especially those with an attractive lilac or pale blue color. Large, rich crystalline aggregates on a rock matrix are also highly valued. Purity and lack of mechanical damage significantly increase the specimen's value. ## Popular Localities The best quality specimens, with distinct crystals, mainly come from localities in Mexico (Durango) and California (USA). The Scawt Hill locality in Northern Ireland is historically important as the discovery site of many rare contact minerals, including spurrite.
Care and storage
## Cleaning Spurrite is sensitive to acids, so it should only be cleaned with lukewarm soapy water and a soft brush. Ultrasonic and steam cleaners should be avoided, as they can damage the brittle mineral. ## What to Avoid The mineral reacts with acids, even weak ones like vinegar or lemon juice, leading to its damage. It should be protected from sudden temperature changes and prolonged exposure to direct sunlight, which can cause fading. ## Storage Due to its brittleness and relatively low hardness, spurrite should be stored separately, in a padded box, to avoid scratches from harder minerals. It is not recommended for setting in everyday jewelry.