Spat
Chemical formula: CaCO₃
Spat, also known as spar, is a general name for minerals with good cleavage, most commonly referring to calcite or fluorite.
Description
## Characteristics Spat is a historical term used to describe minerals that easily break into regular fragments with flat surfaces. It most often refers to calcite, which forms rhombohedral crystals, or fluorite, which crystallizes in cubic or octahedral forms. Spat specimens are characterized by distinct cleavage, which is their main visual feature. Depending on the mineral to which the term "spat" refers, its appearance can vary greatly, from transparent to opaque, with various colors. ## Physical Properties The physical properties of spat are variable and depend on the specific mineral it refers to. For example, calcite (Iceland spar) has a hardness of 3 on the Mohs scale, while fluorite has a hardness of about 4. The luster of spat is usually vitreous, and transparency can range from transparent to opaque. Density also depends on the chemical composition; for calcite, it is about 2.7 g/cm³, and for fluorite, it is about 3.18 g/cm³. ## Colors and Varieties The term "spat" does not refer to a specific mineral, so colors and varieties are very diverse. Calcite can occur in many colors, including colorless, white, yellow, pink, green, blue, brown, and black. Fluorite also exhibits a wide range of colors, such as purple, green, blue, yellow, pink, and even colorless. Varieties of spat are essentially varieties of the minerals it refers to, e.g., Iceland spar (transparent calcite). ## History and Name The name "spat" comes from the German word "Spat," which means a mineral with good cleavage. This term was used by ancient miners and mineralogists to describe minerals that easily split into flat fragments. It does not refer to a specific mineral species but to a certain physical characteristic. In the history of mineralogy, many minerals were referred to as spat before they were precisely classified. ## Applications The applications of "spat" depend on the mineral it refers to. For example, calcite (Iceland spar) is used in optics due to its strong birefringence. Fluorite is used in the chemical industry as a flux and in the production of optical lenses. Spat specimens, especially those with distinct cleavage and attractive color, are also valued by collectors.
Diagnostic features
## Identification Identification of "spat" is primarily based on its distinct cleavage. Minerals referred to by this name, such as calcite or fluorite, easily break into regular fragments. Calcite is characterized by rhombohedral cleavage, and fluorite by octahedral or cubic cleavage. Hardness is also an important diagnostic feature – calcite is soft (3 on the Mohs scale), and fluorite is slightly harder (4 on the Mohs scale). ## Distinguishing from Similar Minerals "Spat" as a general term can be confused with many minerals. Calcite can be distinguished from other white carbonate minerals by its reaction with hydrochloric acid (it effervesces strongly). Fluorite can be distinguished from similar minerals by its lower hardness compared to quartz and its characteristic cleavage. Color and transparency are also helpful but are not decisive features. ## Crystal Forms "Spat" crystals can take various forms, depending on the mineral. Calcite often forms rhombohedra, scalenohedra, or columnar crystals. Fluorite usually occurs in the form of cubes, octahedra, or rhombic dodecahedra. Aggregates can be massive, granular, or form crusts.
Geological environment
## Genesis Minerals referred to as "spat" form in various geological environments. Calcite is very common and forms in sedimentary (limestone, marble), metamorphic, and hydrothermal rocks. Fluorite occurs mainly in hydrothermal veins, in pegmatites, and in sedimentary rocks as cement. Both minerals can also occur in geodes and druses. ## Mineral Associations Calcite often co-occurs with quartz, pyrite, marcasite, barite, celestine, and other carbonate minerals. Fluorite can be found in association with quartz, barite, galena, sphalerite, chalcopyrite, and calcite. ## Localities Known localities for calcite include Iceland (Iceland spar), Mexico, USA (Missouri, Illinois), United Kingdom, Germany, and China. Fluorite occurs in many places around the world, including China, Mexico, USA (Illinois, Kentucky, Colorado), United Kingdom (Derbyshire), Germany (Saxony), and Namibia.
Rarity
Common
Collector aspects
## Quality Criteria Quality criteria for "spat" specimens depend on the specific mineral. For calcite and fluorite, well-formed crystals, intense color, transparency (especially for Iceland spar), and absence of mechanical damage are valued. Large, aesthetic crystal aggregates are also highly sought after. Specimens with rare crystal forms or unusual inclusions are particularly valuable. ## Popular Localities The most prized specimens of Iceland spar (calcite) come from Iceland. High-quality fluorite crystals are found in China, Mexico, USA (especially in Illinois and Kentucky), and the United Kingdom. Specimens with exceptional color, transparency, and size come from these localities.
Care and storage
## Cleaning Cleaning spat specimens, especially calcite and fluorite, requires delicacy. Most specimens can be cleaned with a soft brush and lukewarm water. In the case of calcite, which is sensitive to acids, all acidic cleaning agents should be avoided. Fluorite is relatively soft, so scrubbing should be avoided. ## What to Avoid Spat specimens should be protected from sudden temperature changes, strong impacts, and contact with chemical substances, especially acids in the case of calcite. Prolonged exposure to direct sunlight can cause some varieties of fluorite to fade. High humidity is not usually a problem, but extreme conditions can affect the stability of some minerals. ## Storage Spat specimens are best stored in enclosed display cases or boxes to protect them from dust and mechanical damage. Due to their good cleavage, dropping them should be avoided. Delicate specimens can be wrapped in soft material to prevent scratches. Storing them away from other, harder minerals will prevent damage.