Pimelite
Encyclopedia
Pimelite was discredited as a mineral species by the International Mineralogical Association
(IMA) in 2006, in an article which suggests that “pimelite” specimens are probably willemseite (which is approved), or kerolite
(which is also discredited). This was a mass discreditation, and not based on any re-examination of the type material
(assuming any exists). Nevertheless, a considerable number of papers have been written, verifying that pimelite is a nickel
-dominant smectite. It is always possible to redefine a mineral wrongly discredited.
The mineral was erroneously assumed to be a nickel-rich talc
in a paper published in the American Mineralogist in 1979, but it had already been determined to be a smectite as early as 1938, and this was confirmed in another article in the American Mineralogist in 1966. Both nickel-bearing talc and nickel dominant smectite occur at the type locality
, Szklary, Ząbkowice Śląskie County
, Lower Silesia, Poland.
group, trioctahedral subgroup. (“Smectite” is the name of a group of minerals, not the name of a mineral species).
Subgroup members:
Smectite group minerals are phyllosilicate clay minerals
. Pimelite apparently constitutes part of the mixtures called garnierite
or noumeite, and it could form a series with stevensite or saponite.
It has a molar mass
of 554.5 g.
, and renamed in 1800 by Dietrich Ludwig Gustave Karsten (:de:Dietrich Ludwig Gustav Karsten) from the Greek word for fat, in allusion to the appearance.
, but the crystal class is unknown. As with all phyllosilicates, the basic structural element is a triple layer, called a t-o-t layer, where "t" stands for a tetrahedral sheet and "o" stands for an octahedral sheet. The tetrahedral sheets comprise (Si,Al)O4 tetrahedra , linked together in nearly hexagonal rings. Three of the oxygens
in each tetrahedron form links to other tetrahedra in the sheet, and the fourth oxygen, the apical oxygen, points away from the sheet. The apical oxygens of one tetahedral sheet face the apical oxygens of the other tetrahedral sheet, forming octahedral sites between the sheets, and this is the octahedral "o" layer. The octahedral sites may be fully occupied by divalent
cations
, producing trioctahedral layers, where each O or OH ion is surrounded by 3 divalent cations. Alternatively the octahedral sites may be 2/3 occupied by trivalent
cations
, producing dioctahedral layers, where each O or OH ion is surrounded by 2 trivalent cations. There is one formula unit per unit cell (Z = 1), and the unit cell parameters are a = 5.256 Å and c = 14.822 Å. When treated with glycol the cell expands to 17.35 Å.
and a waxy luster
.
but it can appear isotropic due to its fine grain size. The refractive indices are Nx = 1.592 and Ny = 1.615. It is pleochroic, pale green, and colorless to light yellow green. It is not fluorescent.
, but it shows no cleavage. It is soft with Mohs hardness 2 to 2½, similar to that of gypsum
, and its specific gravity
is 2.23 to 2.98.
It is neither radioactive nor magnetic. It is decomposed by acids.
above serpentinites or dunites
, frequently mixed with nickel
-rich serpentine minerals or quartz
. The type locality is Kosemutz, near Frankenstein, Silesia, Poland, and it has also been found in New Jersey, USA. A nickel silicate
hydroxide
mineral was first described from Franklin, New Jersey
, in 1889, but it has not been reported from the neighbouring Sterling Hill. It was originally called desaulesite, for Major de Saules, manager of the Trotter Mine at Franklin, but that name is now used for zinc
-rich garnierite
. In 1966 the material was shown to be identical with pimelite. Pimelite from the Trotter Shaft occurs as localized, patchy, thin crusts and dense 1 to 6 cm masses as an alteration product of nickel
arsenides
. It is a secondary
, low-temperature mineral, associated with annabergite
, fluorite
, baryte and sphalerite
.
International Mineralogical Association
The International Mineralogical Association is an international group of 38 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 4000 plus known mineral species...
(IMA) in 2006, in an article which suggests that “pimelite” specimens are probably willemseite (which is approved), or kerolite
Kerolite
Kerolite or Cerolite is a metamorphic nickel bearing phyllosilicate mineral similar to talc and serpentine. It has the formula: 3Si4O102·H2O. It is often considered as a talc variety and its official mineral status is uncertain.-References:*...
(which is also discredited). This was a mass discreditation, and not based on any re-examination of the type material
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
(assuming any exists). Nevertheless, a considerable number of papers have been written, verifying that pimelite is a nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
-dominant smectite. It is always possible to redefine a mineral wrongly discredited.
The mineral was erroneously assumed to be a nickel-rich talc
Talc
Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg34 or Mg3Si4O102. In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to fibrous masses, its crystals being so rare as to be almost unknown...
in a paper published in the American Mineralogist in 1979, but it had already been determined to be a smectite as early as 1938, and this was confirmed in another article in the American Mineralogist in 1966. Both nickel-bearing talc and nickel dominant smectite occur at the type locality
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
, Szklary, Ząbkowice Śląskie County
Szklary, Zabkowice Slaskie County
Szklary is a village in the administrative district of Gmina Ząbkowice Śląskie, within Ząbkowice Śląskie County, Lower Silesian Voivodeship, in south-western Poland. Prior to 1945 it was in Germany. It lies approximately north of Ząbkowice Śląskie and south of the regional capital...
, Lower Silesia, Poland.
Mineral group
According to the literature pimelite belongs to the smectiteClay minerals
Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...
group, trioctahedral subgroup. (“Smectite” is the name of a group of minerals, not the name of a mineral species).
Subgroup members:
- hectoriteHectoriteHectorite is a rare soft, greasy, white clay mineralHectorite was first described in 1941 and named for an occurrence in the United States near Hector . Hectorite occurs with bentonite as an alteration product of clinoptilolite from volcanic ash and tuff with a high glass content...
(IMA questionable status) Na0.3(Mg,Li)3Si4O10(OH)2 - pimelite (IMA discredited) Ni3Si4O10(OH)2.4H2O
- saponiteSaponiteSaponite is a trioctahedral mineral of the smectite group. Its chemical formula is Ca0.2532·n. It is soluble in sulfuric acid. It was first described in 1840 by von Svanberg. Varieties of saponite are griffithite, bowlingite and sobotkite.It is soft, massive, and plastic, and exists in veins and...
(Ca,Na)0.3(Mg,Fe2+)3(Si,Al)4O10(OH)2·4H2O - sauconiteSauconiteSauconite is a complex phyllosilicate mineral of the smectite clay group, formula Na0.3Zn34O102·4H2O. It forms soft earthy bluish white to red-brown monoclinic crystals typically massive to micaceous in habit. It has a Mohs hardness of 1 to 2 and a specific gravity of 2.45...
Na0.3Zn3(Si,Al)4O10(OH)2·4H2O - stevensite (IMA questionable status) (Ca0.5,Na)0.33(Mg,Fe++)3Si4O10(OH)2.n(H2O)
- yakhontovite (Ca,Na,K)0.2(Cu,Fe,Mg)2Si4O10(OH)2·3H2O
- zincsilite Zn3Si4O10(OH)2·4H2O
Smectite group minerals are phyllosilicate clay minerals
Clay minerals
Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...
. Pimelite apparently constitutes part of the mixtures called garnierite
Garnierite
Garnierite is a general name for a green nickel ore which is found in pockets and veins within weathered and serpentinized ultramafic rocks. It forms by lateritic weathering of ultramafic rocks and occurs in many nickel laterite deposits in the world. It is an important nickel ore, having a large...
or noumeite, and it could form a series with stevensite or saponite.
It has a molar mass
Molar mass
Molar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...
of 554.5 g.
Discovery
Pimelite was discovered in 1788 by Martin Heinrich KlaprothMartin Heinrich Klaproth
Martin Heinrich Klaproth was a German chemist.Klaproth was born in Wernigerode. During a large portion of his life he followed the profession of an apothecary...
, and renamed in 1800 by Dietrich Ludwig Gustave Karsten (:de:Dietrich Ludwig Gustav Karsten) from the Greek word for fat, in allusion to the appearance.
Structure
It belongs to the hexagonal crystal systemHexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
, but the crystal class is unknown. As with all phyllosilicates, the basic structural element is a triple layer, called a t-o-t layer, where "t" stands for a tetrahedral sheet and "o" stands for an octahedral sheet. The tetrahedral sheets comprise (Si,Al)O4 tetrahedra , linked together in nearly hexagonal rings. Three of the oxygens
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...
in each tetrahedron form links to other tetrahedra in the sheet, and the fourth oxygen, the apical oxygen, points away from the sheet. The apical oxygens of one tetahedral sheet face the apical oxygens of the other tetrahedral sheet, forming octahedral sites between the sheets, and this is the octahedral "o" layer. The octahedral sites may be fully occupied by divalent
Valence (chemistry)
In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...
cations
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
, producing trioctahedral layers, where each O or OH ion is surrounded by 3 divalent cations. Alternatively the octahedral sites may be 2/3 occupied by trivalent
Valence (chemistry)
In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...
cations
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
, producing dioctahedral layers, where each O or OH ion is surrounded by 2 trivalent cations. There is one formula unit per unit cell (Z = 1), and the unit cell parameters are a = 5.256 Å and c = 14.822 Å. When treated with glycol the cell expands to 17.35 Å.
Appearance
Pimelite does not form visible crystals. It is fine-grained or fibrous, with the apple green color typical of nickel compounds. It is translucent, with a white streakStreak (mineralogy)
The streak of a mineral is the color of the powder produced when it is dragged across an unweathered surface. Unlike the apparent color of a mineral, which for most minerals can vary considerably, the trail of finely ground powder generally has a more consistent characteristic color, and is thus...
and a waxy luster
Lustre (mineralogy)
Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning "light", and generally implies radiance, gloss, or brilliance....
.
Optical properties
It is biaxial (-)Birefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
but it can appear isotropic due to its fine grain size. The refractive indices are Nx = 1.592 and Ny = 1.615. It is pleochroic, pale green, and colorless to light yellow green. It is not fluorescent.
Physical properties
Pimelite breaks with an uneven to conchoidal fractureFracture (mineralogy)
In the field of mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a mineral is fractured. Minerals often have a highly distinctive fracture, making it a principal feature used in their identification....
, but it shows no cleavage. It is soft with Mohs hardness 2 to 2½, similar to that 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...
, and its specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
is 2.23 to 2.98.
It is neither radioactive nor magnetic. It is decomposed by acids.
Occurrence
Pimelite is found in lateritic nickel ore depositsLateritic nickel ore deposits
Lateritic nickel ore deposits are surficial, weathered rinds formed on ultramafic rocks.They comprise 73% of the continental world nickel resources and will be in the future the dominant source for the winning of nickel....
above serpentinites or dunites
Dunite
Dunite is an igneous, plutonic rock, of ultramafic composition, with coarse-grained or phaneritic texture. The mineral assemblage is greater than 90% olivine, with minor amounts of other minerals such as pyroxene, chromite and pyrope. Dunite is the olivine-rich end-member of the peridotite group...
, frequently mixed with nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
-rich serpentine minerals or 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,...
. The type locality is Kosemutz, near Frankenstein, Silesia, Poland, and it has also been found in New Jersey, USA. A nickel silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
mineral was first described from Franklin, New Jersey
Franklin, New Jersey
Franklin is a Borough in Sussex County, New Jersey, United States. As of the 2010 United States Census, the borough population was 5,045.Franklin, known as the "Fluorescent Mineral Capital of the World," is located over a rich ore body containing more than 150 minerals, many of them fluorescent and...
, in 1889, but it has not been reported from the neighbouring Sterling Hill. It was originally called desaulesite, for Major de Saules, manager of the Trotter Mine at Franklin, but that name is now used for zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
-rich garnierite
Garnierite
Garnierite is a general name for a green nickel ore which is found in pockets and veins within weathered and serpentinized ultramafic rocks. It forms by lateritic weathering of ultramafic rocks and occurs in many nickel laterite deposits in the world. It is an important nickel ore, having a large...
. In 1966 the material was shown to be identical with pimelite. Pimelite from the Trotter Shaft occurs as localized, patchy, thin crusts and dense 1 to 6 cm masses as an alteration product of nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
arsenides
Arsenide mineral
An arsenide mineral is a mineral that contains arsenide as its main anion. Arsenides are grouped with the sulfides in both the Dana and Strunz mineral classification systems.- Examples :* algodonite Cu6As* domeykite Cu3As* löllingite FeAs2* nickeline NiAs...
. It is a secondary
Supergene (geology)
In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary sulfide ore minerals and...
, low-temperature mineral, associated with annabergite
Annabergite
Annabergite is an arsenate mineral consisting of a hydrous nickelarsenate, Ni32·8H2O, crystallizing in the monoclinic system and isomorphous with vivianite and erythrite. Crystals are minute and capillary and rarely met with, the mineral occurring usually as soft earthy masses and encrustations. A...
, 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...
, baryte and sphalerite
Sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
.