Falcondoite, a member of the

sepiolite Sepiolite, also known in English by the German name meerschaum ( , ; ; meaning "sea foam"), is a soft white clay mineral, often used to make tobacco pipes (known as meerschaum pipes). A complex magnesium silicate, a typical chemical formula for ...

group, was first discovered in the

Dominican Republic The Dominican Republic ( ; es, República Dominicana, ) is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean region. It occupies the eastern five-eighths of the island, which it shares wit ...

, near the town of

Bonao Bonao is a city in the Cibao region of Dominican Republic. It is the capital of the Monseñor Nouel Province, Monseñor Nouel province. The city is located in the center of the country, to the northwest of the national capital Santo Domingo. The ...

. The mineral was found in a deposit mined by Falconbridge Dominica, and so was named "falcondoite" after the company. Falcondoite is frequently associated with sepiolite,

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 ...

talc Talc, or talcum, is a Clay minerals, clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thi ...

, and serpentine, and is commonly

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

-bearing. While the chemical formula for falcondoite can vary, the mineral must contain more nickel than

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

to be considered its own species. The ideal chemical formula for falcondoite is (Ni,Mg)₄Si₆O₁₅(OH)₂·6H₂O.

Occurrence

Falcondoite occurs in an extensive deposit of

laterite Laterite is both a soil and a rock type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by ...

near the town of Bonao in the Dominican Republic. This deposit is part of a serpentinized

harzburgite Harzburgite, an ultramafic, igneous rock, is a variety of peridotite consisting mostly of the two minerals olivine and low-calcium (Ca) pyroxene ( enstatite); it is named for occurrences in the Harz Mountains of Germany. It commonly contains a ...

massif, which is composed of limonitic and serpentinitic ore. It's found in whitish-green veins of garnierite that is rich in sepiolite material. These

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

are often only millimeters to centimeters thick, and can be formed by the infill of tension fractures. Some commonly associated minerals include sepiolite, garnierite, talc, and serpentine. While falcondoite is most closely associated to sepiolite, it's characterized by containing more nickel.

Physical properties

Falcondoite is a whitish-green to green colored translucent mineral with a resinous luster and a white streak. It exhibits a hardness of 2–3 on the

Mohs hardness scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

. Falcondoite is a

brittle A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Bre ...

and

friable Friability ( ), the condition of being friable, describes the tendency of a solid substance to break into smaller pieces under duress or contact, especially by rubbing. The opposite of friable is indurate. Substances that are designated hazardous, ...

mineral with distinct cleavage. It occurs as aggregates of microscopic, fibrous crystals that are typically smaller than 10 μm in size, which have a refractive index of less than 1.55. Under cross-polarized light, these crystals experience extinction parallel or nearly parallel with positive elongation along the c-axis. The mineral has a measured

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

of 1.9 g/cm³ and a

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...

of 1.9.

Chemical properties

Falcondoite is considered to be a variety of

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

-like, nickel-bearing hydrous

silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

, which is a common component of garnierite mineralization. It is categorized as a

phyllosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

whose structure consists of single tetrahedral sheets of six-membered rings that are connected by octahedral sheets or bands. Falcondoite and sepiolite form a solid solution series of garnierite, with sepiolite being characterized as containing more magnesium, while falcondoite generally contains more nickel. Falcondoite's chemical formula can range from i₈Si₁₂O₃₀(OH)₄(OH₂)₄·8(H₂O)to Ni₄Mg₄)Si₁₂O₃₀(OH)₄(OH₂)₄·8(H₂O)with the weight percent of

NiO are two wrathful and muscular guardians of the Gautama Buddha, Buddha standing today at the entrance of many Buddhist temples in East Asian Buddhism in the form of frightening wrestler-like statues. They are dharmapala manifestations of the bo ...

being up to 38.03%. Some common impurities of falcondoite include

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...

, and

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

Chemical composition

Crystallographic properties

Falcondoite is in the orthorhombic

crystal system In crystallography, a crystal system is a set of point groups (a group of geometric symmetries with at least one fixed point). A lattice system is a set of Bravais lattices. Space groups are classified into crystal systems according to their po ...

, with

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...

Pncn. The unit cell dimensions are a = 13.5 Å, b = 26.9 Å, c = 5.24 Å, and α = 90°, β = 90°, γ = 90°. The standard unit cell volume is equal to 1903 Å³. Falcondoite is biaxial positive with a refractive index value of 1.55, and a

birefringence Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefring ...

of δ=0.01 - 0.02.

X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

analysis of falcondoite shows a pattern similar to that of sepiolite. Some of the measured peaks end up broadened possibly due to poor crystallinity, so accurate d-values were difficult to obtain. Powder X-Ray Diffraction data:

References