sedimentary
Microcrystalline Limestone
Limestone (CaCO3 with impurities)
Hardness: 3 (Mohs scale), Color: Dull gray, Luster: Earthy, Crystal system: Hexagonal (microscopic calcite crystals), Clavage: None, Texture: Fine-grained/aphanitic
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Physical properties
Hardness: 3 (Mohs scale), Color: Dull gray, Luster: Earthy, Crystal system: Hexagonal (microscopic calcite crystals), Clavage: None, Texture: Fine-grained/aphanitic
Formation & geological history
Formed by the accumulation of shell, coral, algal and fecal debris in marine environments. It can also be precipitated from calcium-rich water. Common in ancient reef beds and shallow sea basins.
Uses & applications
Primary source of lime for cement, used as a building stone, crushed for road base, and used in the manufacturing of glass and steel. Small pieces have little commercial value.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is susceptible to acid rain, which can dissolve the rock over long periods of time, leading to the formation of caves and sinkholes.
Field identification & locations
Identified in the field by its gray color and fine texture; it will effervesce (fizz) vigorously when a drop of dilute hydrochloric acid or strong vinegar is applied. Found globally in sedimentary basins.
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