Huttonite
Encyclopedia
Huttonite is a thorium
nesosilicate mineral
with the chemical formula 4 and which crystallizes in the monoclinic system
. It is dimorphous
with tetragonal thorite
, and isostructual with monazite
. An uncommon mineral, huttonite forms transparent or translucent cream–colored crystals. It was first identified in samples of beach sands from the West Coast
region of New Zealand
by the mineralogist Colin Osborne Hutton. Owing to its rarity, huttonite is not an industrially useful mineral.
deposits in South Westland
, New Zealand, where it was found as anhedral
grains of no more than 0.2 mm maximum dimension. It is most prevalent in the sand at Gillespie's Beach, near Fox Glacier
, which is the type location
, where it is accompanied by scheelite
, cassiterite
, zircon
, uranothorite, ilmenite
and gold
. It was found at a further six nearby locations in less plentiful amounts. Huttonite was extracted from the sands by first fractionating in iodomethane
and then electromagnetically. Pure samples were subsequently obtained by handpicking huttonite grains under a microscope. This was accomplished either in the presence of short wave (2540 Å) fluorescent light, where the dull white fluorescence distinguishes it from scheelite (fluoresces blue) and zircon (fluoresces yellow), or by first boiling the impure sample in hydrochloric acid
to induce an oxide surface on scheelite and permitting handpicking under visible light.
Hutton suggested the huttonite contained in the beach sand and fluvio-glacial deposits originated from Otago
schist
s or pegmatitic veins
in the Southern Alps
.
In addition to New Zealand
, huttonite has been found in granitic pegmatite
s of Bogatynia, Poland
, where it associated with cheralite, thorogummite, and ningyoite; and in nepheline syenite
s of Brevik, Norway
.
nesosilicate with the chemical formula 4. It is composed (by weight) of 71.59% thorium, 19.74% oxygen, and 8.67% silicon. Huttonite is found very close to its ideal stoichiometric
composition, with impurities contributing less than 7% mole fraction. The most significant impurities to be observed are 2 and 25.
Huttonite crystallizes in the monoclinic system with space group
P21/n. The unit cell contains four ThSiO4 units, and has dimensions a = 6.784 ± 0.002Å, b = 6.974 ± 0.003Å, c = 6.500 ± 0.003Å, and inter–axis angle β = 104.92 ± 0.03o. The structure is that of a nesosilicate — discrete SiO42− tetrahedra coordinating thorium ions. Each thorium has coordination number
nine. Axially, four oxygen atoms, representing the edges of two SiO4 monomers on opposite sides of the thorium atom, form a (–SiO4–Th–) chain parallel to the c axis. Equatorially, five nearly planar oxygen atoms representing vertices of distinct silicate tetrahedra coordinate each thorium. The lengths of the axial Th–O bonds are 2.43 Å, 2.51 Å, 2.52 Å, 2.81 Å, and of the equatorial bonds, 2.40 Å, 2.41 Å, 2.41 Å, 2.50 Å, and 2.58 Å. The Si–O bonds are nearly equal, with lengths 1.58 Å, 1.62 Å, 1.63 Å, and 1.64 Å.
Huttonite is isostructural with monazite
. Substitution of the rare earth element
s and phosphorus of monazite with thorium and silicon of huttonite can occur to generates a solid solution
. At the huttonite end-member, continuous rare earth substitution of thorium of up to 20% by weight has been observed. Thorium substitution in monazite has been observed up to 27% by weight. Substitution of PO4 for SiO4 also occurs associated with the introduction of fluoride
, hydroxide
, and metal ions.
Huttonite is dimorphic
with thorite
. Thorite crystallizes in a higher symmetry and lower density tetragonal form in which the thorium atoms coordinate to one less oxygen atom in an octahedral arrangement. Thorite is stable at lower temperatures than huttonite; at 1 atmosphere, the thorite–huttonite phase transition occurs between 1210 and 1225 °C. With increasing pressure the transition temperature increases. This relatively high transition temperature is thought to explain the relative rarity of huttonite on the Earth's crust. Unlike thorite, huttonite is not affected by metamictization
.
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
nesosilicate mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
with the chemical formula 4 and which crystallizes in the monoclinic system
Monoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
. It is dimorphous
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
with tetragonal thorite
Thorite
Thorite, SiO4, is a rare nesosilicate of thorium that crystallizes in the tetragonal system and is isomorphous with zircon and hafnon. It is the most common mineral of thorium and is nearly always strongly radioactive. It was named in 1829 to reflect its thorium content...
, and isostructual with monazite
Monazite
Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...
. An uncommon mineral, huttonite forms transparent or translucent cream–colored crystals. It was first identified in samples of beach sands from the West Coast
West Coast, New Zealand
The West Coast is one of the administrative regions of New Zealand, located on the west coast of the South Island, and is one of the more remote and most sparsely populated areas of the country. It is made up of three districts: Buller, Grey and Westland...
region of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
by the mineralogist Colin Osborne Hutton. Owing to its rarity, huttonite is not an industrially useful mineral.
Occurrence
Huttonite was first described in 1950 from beach sand and fluvio-glacialFluvio-glacial
Fluvio-glacial is the water created by the melting of glaciers. It literally means "Water Glacier." It is also commonly called melt water.Fluvio-glacial can also mean sediments deposited by the glacier meltwater....
deposits in South Westland
Westland District
Westland District is a territorial authority on the west coast of New Zealand's South Island. Its population is - Government :The Westland District is governed by an elected Council, headed by an elected Mayor. The Mayor is elected at large. The current Mayor is Maureen Pugh. Councillors are...
, New Zealand, where it was found as anhedral
Euhedral
Euhedral crystals are those that are well-formed with sharp, easily recognised faces. Normally, crystals do not form smooth faces or sharp crystal outlines. Many crystals grow from cooling liquid magma...
grains of no more than 0.2 mm maximum dimension. It is most prevalent in the sand at Gillespie's Beach, near Fox Glacier
Fox Glacier
The Fox Glacier is a long glacier located in Westland Tai Poutini National Park on the West Coast of New Zealand's South Island...
, which is the type location
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....
, where it is accompanied by scheelite
Scheelite
Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws...
, cassiterite
Cassiterite
Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem...
, zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
, uranothorite, ilmenite
Ilmenite
Ilmenite is a weakly magnetic titanium-iron oxide mineral which is iron-black or steel-gray. It is a crystalline iron titanium oxide . It crystallizes in the trigonal system, and it has the same crystal structure as corundum and hematite....
and gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
. It was found at a further six nearby locations in less plentiful amounts. Huttonite was extracted from the sands by first fractionating in iodomethane
Iodomethane
Methyl iodide, also called iodomethane, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one hydrogen atom by an atom of iodine. It is naturally...
and then electromagnetically. Pure samples were subsequently obtained by handpicking huttonite grains under a microscope. This was accomplished either in the presence of short wave (2540 Å) fluorescent light, where the dull white fluorescence distinguishes it from scheelite (fluoresces blue) and zircon (fluoresces yellow), or by first boiling the impure sample in hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
to induce an oxide surface on scheelite and permitting handpicking under visible light.
Hutton suggested the huttonite contained in the beach sand and fluvio-glacial deposits originated from Otago
Otago
Otago is a region of New Zealand in the south of the South Island. The region covers an area of approximately making it the country's second largest region. The population of Otago is...
schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
s or pegmatitic veins
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....
in the Southern Alps
Southern Alps
The Southern Alps is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the island's western side...
.
In addition to New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, huttonite has been found in granitic pegmatite
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....
s of Bogatynia, Poland
Bogatynia
Bogatynia is a town in Zgorzelec County, Lower Silesian Voivodeship, in south-western Poland, close to the tripoint of the Czech, German and Polish borders. The town lies approximately south of Zgorzelec, and west of the regional capital Wrocław. As of 2006 it had 19,068 inhabitants.The...
, where it associated with cheralite, thorogummite, and ningyoite; and in nepheline syenite
Nepheline syenite
Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites, but dark green varieties are also known...
s of Brevik, Norway
Brevik
is a town in Telemark, Norway with an estimated population of 2,700. Brevik was established as a municipality January 1, 1838 , but was merged with Porsgrunn on January 1, 1964. Brevik is regarded one of the best preserved towns from the sailing ship era...
.
Structure
Huttonite is a thoriumThorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
nesosilicate with the chemical formula 4. It is composed (by weight) of 71.59% thorium, 19.74% oxygen, and 8.67% silicon. Huttonite is found very close to its ideal stoichiometric
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...
composition, with impurities contributing less than 7% mole fraction. The most significant impurities to be observed are 2 and 25.
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...
P21/n. The unit cell contains four ThSiO4 units, and has dimensions a = 6.784 ± 0.002Å, b = 6.974 ± 0.003Å, c = 6.500 ± 0.003Å, and inter–axis angle β = 104.92 ± 0.03o. The structure is that of a nesosilicate — discrete SiO42− tetrahedra coordinating thorium ions. Each thorium has coordination number
Coordination number
In chemistry and crystallography, the coordination number of a central atom in a molecule or crystal is the number of its nearest neighbours. This number is determined somewhat differently for molecules and for crystals....
nine. Axially, four oxygen atoms, representing the edges of two SiO4 monomers on opposite sides of the thorium atom, form a (–SiO4–Th–) chain parallel to the c axis. Equatorially, five nearly planar oxygen atoms representing vertices of distinct silicate tetrahedra coordinate each thorium. The lengths of the axial Th–O bonds are 2.43 Å, 2.51 Å, 2.52 Å, 2.81 Å, and of the equatorial bonds, 2.40 Å, 2.41 Å, 2.41 Å, 2.50 Å, and 2.58 Å. The Si–O bonds are nearly equal, with lengths 1.58 Å, 1.62 Å, 1.63 Å, and 1.64 Å.
Huttonite is isostructural with monazite
Monazite
Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...
. Substitution of the rare earth element
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
s and phosphorus of monazite with thorium and silicon of huttonite can occur to generates a solid solution
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...
. At the huttonite end-member, continuous rare earth substitution of thorium of up to 20% by weight has been observed. Thorium substitution in monazite has been observed up to 27% by weight. Substitution of PO4 for SiO4 also occurs associated with the introduction of fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
, 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...
, and metal ions.
Huttonite is dimorphic
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
with thorite
Thorite
Thorite, SiO4, is a rare nesosilicate of thorium that crystallizes in the tetragonal system and is isomorphous with zircon and hafnon. It is the most common mineral of thorium and is nearly always strongly radioactive. It was named in 1829 to reflect its thorium content...
. Thorite crystallizes in a higher symmetry and lower density tetragonal form in which the thorium atoms coordinate to one less oxygen atom in an octahedral arrangement. Thorite is stable at lower temperatures than huttonite; at 1 atmosphere, the thorite–huttonite phase transition occurs between 1210 and 1225 °C. With increasing pressure the transition temperature increases. This relatively high transition temperature is thought to explain the relative rarity of huttonite on the Earth's crust. Unlike thorite, huttonite is not affected by metamictization
Metamictization
Metamictization is a natural process resulting in the gradual and ultimately complete destruction of a mineral's crystal structure, leaving the mineral amorphous...
.