Pezzottaite, marketed under the name raspberyl or raspberry beryl, is a

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

species first recognized by the International Mineralogical Association in September 2003. Pezzottaite is a caesium analogue of

beryl Beryl ( ) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several ...

, a silicate of caesium,

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form m ...

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...

and

aluminium 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. I ...

, with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

Cs(Be₂Li)Al₂Si₆O₁₈. Named after

Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance language *** Regional Ita ...

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althoug ...

and

mineralogist Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proce ...

Federico Pezzotta, pezzottaite was first thought to be either

red beryl Red beryl, formerly known as bixbite and marketed as red emerald or scarlet emerald, is an extremely rare variety of beryl as well as one of the rarest minerals on Earth. The gem gets its red color from manganese ions embedded inside of beryllium ...

or a new variety of beryl ("caesium beryl"); unlike actual beryl, however, pezzottaite contains lithium and

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...

lizes in the

trigonal In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal ...

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 poin ...

rather than the

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A '' regular hexagon'' has ...

system. Colors include shades of raspberry red to

orange-red Vermilion (sometimes vermillion) is a color, color family, and pigment most often made, since ancient history, antiquity until the 19th century, from the powdered mineral cinnabar (a form of mercury sulfide, which is toxic) and its correspondi ...

and

pink Pink is the color of a namesake flower that is a pale tint of red. It was first used as a color name in the late 17th century. According to surveys in Europe and the United States, pink is the color most often associated with charm, politeness, ...

. Recovered from miarolitic cavities in the

granitic A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz- ...

pegmatite fields of

Fianarantsoa province Fianarantsoa Province is a former province of Madagascar. It has an area of 103,272 km2 and population of 3,366,291 (July 2001 estimate). Its capital was Fianarantsoa. The province along with the 5 other was abolished in 2007 in favour of cre ...

, southern

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

, the pezzottaite crystals were small—no more than about in their widest dimension—and tabular or equant in

habit A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.

, and few in number, most being heavily included with growth tubes and liquid feathers. Approximately 10 per cent of the rough material would also exhibit

chatoyancy In gemology, chatoyancy ( ), or chatoyance or cat's eye effect, is an optical reflectance effect seen in certain gemstones, woods, and carbon fibre. Coined from the French "œil de chat", meaning "cat's eye", chatoyancy arises either from the ...

when polished. Most cut pezzottaite gems are under one carat (200 mg) in weight and rarely exceed two carats (400 mg). With the exception of hardness (8 on

Mohs 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 ...

), the physical and optical properties of pezzottaite—i.e.,

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 at its densest ...

3.10 (average),

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

1.601 to 1.620, birefringence 0.008 to 0.011 (uniaxial negative)—are all higher than typical beryl. Pezzottiate is brittle with a conchoidal to irregular fracture, and streaks white. Like beryl, it has an imperfect to fair basal cleavage.

Pleochroism Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgrou ...

is moderate, from pink-orange or purplish pink to pinkish purple. Pezzottaite's absorption spectrum, as seen by a hand-held (direct vision)

spectroscope An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...

, features a band at 485–500 nm with some specimens showing additional weak lines at 465 and 477 nm and a weak band at 550 to 580 nm. Most (if not all) of the Madagascan deposits have since been exhausted. Pezzottaite has been found in at least one other locality, Afghanistan: this material was first thought to be caesium-rich

morganite Morganite is an orange or pink gemstone and is also a variety of beryl. Morganite can be mined in countries like Brazil, Afghanistan, Mozambique, Namibia, the United States, and Madagascar. Morganite has grown in popularity since 2010. ''Brides ...

(pink beryl). Like morganite and bixbite, pezzottaite is believed to owe its color to radiation-induced color centres involving trivalent

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

. Pezzottaite will lose its color if heated to 450 °C for two hours, but the color can be restored with gamma irradiation.

References

{{Lithium compounds Lithium minerals Beryllium minerals Cyclosilicates Gemstones Trigonal minerals Minerals in space group 161 Caesium minerals Beryl group

See also

References