Coyoteite
Encyclopedia
Coyoteite is a hydrated sodium
iron
sulfide mineral
. The mineral was named coyoteite after Coyote Peak near Orick, California
where it was discovered (along with another rare mineral, orickite).
This mineral is unstable under normal atmospheric conditions, making it rare at the surface. The mineral was first described in a petrographic
study of a sample of a mafic
diatreme
at Coyote Peak. The largest piece of coyoteite found on that specimen has the dimensions of 0.2 × 0.4 mm.
. The total concentration of detected elements was less than 100% (90.7 weight percent). Qualitative analyses and TAP crystal were used to find the missing 9.31%. The results confirmed the missing elements to be hydrogen
and oxygen
, which are undetectable by the electron microprobe. It was unclear however whether the hydrogen and oxygen are in the form of water or a hydroxide.
The mineral is insoluble in cold acids, such as HCl, but dissolves upon heating.
on the {111} planes and shows a unique chevron pattern because of the diametrical arrangement of these crystallographically equivalent cleavage planes. The measured density
is 2.5 to 2.6 g/cm3 and the calculated one is 2.879 g/cm3. This significant density difference is because of the presence of epoxy
between the cleavage planes. The hardness is 1.5 on Mohs scale and is comparable to that of erdite (NaFeS2·2H2O) which has a similar chemical composition. Coyoteite is moderately magnetic. On the polished thin section, coyoteite is pale brownish to gray, with pink tint. It shows low pleochroism
, from gray to pink. In reverse, it shows large optical anisotropy, from gray to dull golden orange.
classifies the coyoteite crystal system
as triclinic. The crystal belongs to P1 or P space group
and to 1 or point group
. Imaging shows that coyoteite has poor crystal quality. The X-ray diffraction pattern suggests the following value for the crystallographic axes
a = 7.409 Å
, b = 9.881 Å, c = 6.441 Å; α = 100° 25’, β = 104° 37’ and γ = 81° 29’; the unit cell volume is V = 446.2 Å3.
at the Coyote Peak near Orick
, Humboldt County, California
, USA. It is formed in pegmatitic
clots associated with some rare iron sulfide minerals, such as erdite, bartonite and djerfisherite, as well as with common minerals pyrrhotite
and magnetite
.
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
sulfide mineral
Sulfide mineral
The sulfide minerals are a class of minerals containing sulfide as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts...
. The mineral was named coyoteite after Coyote Peak near Orick, California
Orick, California
Orick is a census-designated place situated on the banks of the Redwood Creek in Humboldt County, California. It is located north of Eureka, at an elevation of 26 feet . The ZIP Code is 95555...
where it was discovered (along with another rare mineral, orickite).
This mineral is unstable under normal atmospheric conditions, making it rare at the surface. The mineral was first described in a petrographic
Petrography
Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. Petrographic descriptions start with the field notes at the...
study of a sample of a mafic
Mafic
Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...
diatreme
Diatreme
A diatreme is a breccia-filled volcanic pipe that was formed by a gaseous explosion. Diatremes often breach the surface and produce a tuff cone, a filled relatively shallow crater known as a maar, or other volcanic pipes.- Word origin :...
at Coyote Peak. The largest piece of coyoteite found on that specimen has the dimensions of 0.2 × 0.4 mm.
Chemical composition and properties
The chemical formula of the mineral is NaFe3S5·2H2O. It was obtained by the analysis of five grains using the 10-kV EMX-SM electron microprobeElectron microprobe
An electron microprobe , also known as an electron probe microanalyzer or electron micro probe analyzer , is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials...
. The total concentration of detected elements was less than 100% (90.7 weight percent). Qualitative analyses and TAP crystal were used to find the missing 9.31%. The results confirmed the missing elements to be hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and oxygen
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...
, which are undetectable by the electron microprobe. It was unclear however whether the hydrogen and oxygen are in the form of water or a hydroxide.
The mineral is insoluble in cold acids, such as HCl, but dissolves upon heating.
Physical and optical properties
Coyoteite is black in color and is streaked with opaque metallic luster in fragmental samples. The mineral has perfect cleavageCleavage (crystal)
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...
on the {111} planes and shows a unique chevron pattern because of the diametrical arrangement of these crystallographically equivalent cleavage planes. The measured density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
is 2.5 to 2.6 g/cm3 and the calculated one is 2.879 g/cm3. This significant density difference is because of the presence of epoxy
Epoxy
Epoxy, also known as polyepoxide, is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives....
between the cleavage planes. The hardness is 1.5 on Mohs scale and is comparable to that of erdite (NaFeS2·2H2O) which has a similar chemical composition. Coyoteite is moderately magnetic. On the polished thin section, coyoteite is pale brownish to gray, with pink tint. It shows low pleochroism
Pleochroism
Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles with polarized light.- Background :Anisotropic crystals will have optical properties that vary with the direction of light...
, from gray to pink. In reverse, it shows large optical anisotropy, from gray to dull golden orange.
Crystallography
The X-Ray precession imageX-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
classifies the coyoteite crystal system
Crystal system
In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals...
as triclinic. The crystal belongs to P1 or P space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
and to 1 or point group
Point group
In geometry, a point group is a group of geometric symmetries that keep at least one point fixed. Point groups can exist in a Euclidean space with any dimension, and every point group in dimension d is a subgroup of the orthogonal group O...
. Imaging shows that coyoteite has poor crystal quality. The X-ray diffraction pattern suggests the following value for the crystallographic axes
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
a = 7.409 Å
Ångström
The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
, b = 9.881 Å, c = 6.441 Å; α = 100° 25’, β = 104° 37’ and γ = 81° 29’; the unit cell volume is V = 446.2 Å3.
Possible atomic structure
Scarcity of coyoteite hinders attempts to determine its atomic structure. It is unknown whether the oxygen and the hydrogen are present in the mineral as H2O molecules or OH− anions. However, because of the softness and the lamellar cleavage in the mineral, coyoteite structure might be close to that of valleriite (4(Fe,Cu)S·3(Mg,Al)(OH)2). Valleriite is a layered mineral, it consists of layers of (Mg0.68Al0.32(OH)2) and layers of (Fe0.07Cu0.93S2).Geologic occurrence
Coyoteite has been found only in the mafic alkalic diatremeDiatreme
A diatreme is a breccia-filled volcanic pipe that was formed by a gaseous explosion. Diatremes often breach the surface and produce a tuff cone, a filled relatively shallow crater known as a maar, or other volcanic pipes.- Word origin :...
at the Coyote Peak near Orick
Orick, California
Orick is a census-designated place situated on the banks of the Redwood Creek in Humboldt County, California. It is located north of Eureka, at an elevation of 26 feet . The ZIP Code is 95555...
, Humboldt County, California
Humboldt County, California
Humboldt County is a county in the U.S. state of California, located on the far North Coast 200 miles north of San Francisco. According to 2010 Census Data, the county’s population was 134,623...
, USA. It is formed in pegmatitic
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
clots associated with some rare iron sulfide minerals, such as erdite, bartonite and djerfisherite, as well as with common minerals pyrrhotite
Pyrrhotite
Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...
and magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
.