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| Pezzottaite | |
|---|---|
 | |
| General | |
| Category | Cyclosilicateminerals |
| Formula | Cs(Be2Li)Al2Si6O18 |
| IMA symbol | Pez[1] |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) (sameH-M symbol) |
| Space group | R3c |
| Identification | |
| Color | Raspberry red, orange-red, pink |
| Crystal habit | Flattened, tabular, equant, aggregate |
| Cleavage | Imperfect; basal |
| Fracture | Conchoidal to uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 8 |
| Luster | Vitreous |
| Streak | White |
| Specific gravity | 3.10 |
| Optical properties | Uniaxial |
| Refractive index | 1.601 to 1.620 |
| Birefringence | −0.008 to 0.011 |
| Pleochroism | Moderate dichroic |
| References | [2][3][4] |
Pezzottaite, marketed under the nameraspberyl orraspberry beryl, is amineral species first recognized by theInternational Mineralogical Association in September 2003.[5] Pezzottaite is acaesium analogue ofberyl, asilicate of caesium,beryllium,lithium andaluminium, with thechemical formula Cs(Be2Li)Al2Si6O18. Named afterItaliangeologist andmineralogist Federico Pezzotta, pezzottaite was first thought to be eitherred beryl or a new variety of beryl ("caesium beryl"); unlike actual beryl, however, pezzottaite contains lithium andcrystallizes in thetrigonalcrystal system rather than thehexagonal system.
Colors include shades ofraspberry red toorange-red andpink. Recovered frommiarolitic cavities in thegraniticpegmatite fields ofFianarantsoa province, southernMadagascar, the pezzottaite crystals were small—no more than about 7 cm (2.8 in) in their widest dimension—and tabular or equant inhabit, and few in number, most being heavily included with growth tubes and liquid feathers. Approximately 10 percent of the rough material would also exhibitchatoyancy when polished. Most cut pezzottaite gems are under onecarat (200 mg) in weight and rarely exceed two carats (400 mg).
With the exception of hardness (8 onMohs scale), the physical and optical properties of pezzottaite—i.e.,specific gravity 3.10 (average),refractive index 1.601 to 1.620,birefringence 0.008 to 0.011 (uniaxial negative)—are all higher than typical beryl. Pezzottiate is brittle with aconchoidal to irregularfracture, and streaks white. Like beryl, it has an imperfect to fair basalcleavage.Pleochroism is moderate, from pink-orange or purplish pink to pinkish purple. Pezzottaite'sabsorption spectrum, as seen by a hand-held (direct vision)spectroscope, 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.
The mineral was recovered from granitic pegmatite fields of Fianarantsoa province, southern Madagascar. 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-richmorganite (pink beryl). Like morganite and red beryl, pezzottaite is believed to owe its color toradiation-inducedcolor centres involving trivalentmanganese. Pezzottaite will lose its color if heated to 450 °C for two hours, but the color can be restored withgamma irradiation.
