Spar is an old mining or mineralogy term used to refer to

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

s that have readily discernible faces. A spar will easily break or cleave into

rhomboid Traditionally, in two-dimensional geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are non-right angled. The terms "rhomboid" and "parallelogram" are often erroneously conflated with each oth ...

al, cubical, or laminated fragments with smooth shiny surfaces. The various spar minerals were a historical term among miners and alchemists for any nonmetallic mineral akin to

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

, known in Old English as spærstān, ''spear stone'', referring to its crystalline projections. Thus, the word spar in mineralogy has the same root as "spear,". Amongst

miner A miner is a person who extracts ore, coal, chalk, clay, or other minerals from the earth through mining. There are two senses in which the term is used. In its narrowest sense, a miner is someone who works at the rock face (mining), face; cutt ...

s the term "spar" today is frequently used alone to express any bright crystalline substance. Most frequently, spar describes easily cleaved, lightly colored nonmetallic minerals such as

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

or baryte. Baryte ( Ba S O₄), the main source of barium, is also called "heavy spar" ( Greek "barys" means "heavy"). Calcite often forms the dogtooth spar crystals found in vugs and

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

Formation underwater

Generally, a spar will form underwater, either in a

phreatic zone The phreatic zone, saturated zone, or zone of saturation, is the part of an aquifer, below the water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractur ...

, or below the

water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...

, the essential place where most caves form, or in standing pools, as pool spar. If a cave floods and a pool forms, that submerges stalactites, a formation known as bottlebrushes may form. Mineral component ions dissolved in water are mostly deposited as minerals such as

and

, and sometimes even halite,

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

, and fluorite, through the course of thousands of years, building up on each other.

Formation in the air

Sometimes, spar will form in the air due to solutions seeping out of the cave's walls or through porous sediments. When grown in the air, it is often made of

or selenite. Sometimes it will form as small needles found in sediments. Other spars can be found on the tips of

chandeliers.

References

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External links

Virtual cave tour
Crystals Mineralogy Cave geology

Formation underwater

Formation in the air

See also

References

External links