Spar (mineralogy)
Encyclopedia
Spar is a term that is used to refer to a category of crystal
s that have readily discernible faces. Crystal
lized, earthy, and some metallic, a spar will easily break into rhomboid
al, cubical
, or laminated fragments with polished surfaces, but without regard to the ingredients of which they are composed.
The various "spar" minerals were a historical term among miners and alchemists for any nonmetallic mineral akin to gypsum
, 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," by way of comparison to gypsum, as a common natural crystal forming in spearlike projections.
Amongst miner
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
, calcite
or barite
. Barite (Ba
S
O
4), the main source of barium
, is also called "heavy spar" (Greek
"barys" means "heavy").
The largest type of spar is of the phreatic variety, since it essentially much more time to grow than average spar. It grows best where the water is just barely saturated with minerals. Some caves are like giant geode
s, the walls and ceilings completely lined with spar. Jewel Cave and others in the Black Hills
of South Dakota
contain large quantities of spar.
, or below the water table
, the essential place where most caves form. Minerals in the water, mostly calcite
or gypsum
, but sometimes even halite
, quartz
, and fluorite
, are deposited through the course of thousands of years, building up on each other.
s seeping out of the cave's walls or through porous sediments. When grown in the air, it is often made of gypsum
or selenite. Sometimes it will form as small needles found in sediments. Others spar can be found on the tips of gypsum
chandeliers.
. Often the pool in which the crystals grew has evaporated, or fills only seasonally. Pool spar is often found on the bottom of shelfstone
.
Most pool spar is nicknamed "dogtooth" because it comes to a jagged point. Other pool spar, especially ones formed along the flat surface of the pool, may even form in a triangular shape.
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
s that have readily discernible faces. Crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
lized, earthy, and some metallic, a spar will easily break into rhomboid
Rhomboid
Traditionally, in two-dimensional geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are oblique.A parallelogram with sides of equal length is a rhombus but not a rhomboid....
al, cubical
Cube
In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex. The cube can also be called a regular hexahedron and is one of the five Platonic solids. It is a special kind of square prism, of rectangular parallelepiped and...
, or laminated fragments with polished surfaces, but without regard to the ingredients of which they are composed.
The various "spar" minerals were a historical term among miners and alchemists for any nonmetallic mineral akin to gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
, 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," by way of comparison to gypsum, as a common natural crystal forming in spearlike projections.
Amongst miner
Miner
A miner is a person whose work or business is to extract ore or minerals from the earth. Mining is one of the most dangerous trades in the world. In some countries miners lack social guarantees and in case of injury may be left to cope without assistance....
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
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
, calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
or barite
Barite
Baryte, or barite, is a mineral consisting of barium sulfate. The baryte group consists of baryte, celestine, anglesite and anhydrite. Baryte itself is generally white or colorless, and is the main source of barium...
. Barite (Ba
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
S
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
4), the main source of barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
, is also called "heavy spar" (Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
"barys" means "heavy").
The largest type of spar is of the phreatic variety, since it essentially much more time to grow than average spar. It grows best where the water is just barely saturated with minerals. Some caves are like giant geode
Geode
Geodes are geological secondary sedimentary structures which occur in sedimentary and certain volcanic rocks. Geodes are essentially spherical masses of mineral matter that were deposited sygenetically within the rock formations they are found in. Geodes have a Chalcedony shell containing...
s, the walls and ceilings completely lined with spar. Jewel Cave and others in the Black Hills
Black Hills
The Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, USA. Set off from the main body of the Rocky Mountains, the region is something of a geological anomaly—accurately described as an "island of...
of South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
contain large quantities of spar.
Formation
Generally, a spar will form underwater, either in a phreatic zonePhreatic
The term phreatic is used in Earth sciences to refer to matters relating to ground water below the water table . The term 'phreatic surface' indicates the location where the pore water pressure is under atmospheric conditions...
, or below the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
, the essential place where most caves form. Minerals in the water, mostly calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
or gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
, but sometimes even halite
Halite
Halite , commonly known as rock salt, is the mineral form of sodium chloride . Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on the amount and type of impurities...
, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, and fluorite
Fluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...
, are deposited through the course of thousands of years, building up on each other.
Growth in the air
Sometimes, spar will form in the air due to solutionSolution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
s seeping out of the cave's walls or through porous sediments. When grown in the air, it is often made of gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
or selenite. Sometimes it will form as small needles found in sediments. Others spar can be found on the tips of gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
chandeliers.
Pool spar
Pool spar are well-defined crystals that grow underwater in pools, and are a subtype of spar crystal, usually composed of calciteCalcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
. Often the pool in which the crystals grew has evaporated, or fills only seasonally. Pool spar is often found on the bottom of shelfstone
Shelfstone
Shelfstone is a type of speleothem that grows inwards from the edge of a cave pool. It takes the form of ledges that tend to be flat on top and sloping undernerth. They are almost always formed from calcite, when materials precipitated from dripping water onto a cave pool attach to the side. The...
.
Most pool spar is nicknamed "dogtooth" because it comes to a jagged point. Other pool spar, especially ones formed along the flat surface of the pool, may even form in a triangular shape.