Beryl

cyclosilicate

aquamarine

Formula: Be3Al2Si6O18 cyclosilicate (ring silicate)
Specific gravity: 2.63 to 2.92
Hardness: 7½ to 8
Streak: White
Colour: Pure beryl is colourless, but it occurs in many different colours due to impurities. Goshenite is the colourless, gemmy variety of beryl. The blue-green colour of aquamarine is caused by trivalent iron Fe3+ and divalent iron Fe2+ in different positions in the crystal lattice. The golden yellow colour of heliodor is caused by trivalent iron Fe3+; the green of emerald is caused by chromium and/or vanadium; the pink of morganite is caused by small amounts of manganese and the deep red of red beryl is also caused by trivalent manganese Mn3+ (Munich 2015, Extra Lapis 7.22-23).
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Plutonic igneous environments
Pegmatites (typical)
Metamorphic environments

Beryl, although containing the rare element Be, is rather common and widely distributed. It occurs usually in granitic rocks, or in pegmatites. It is also found in mica schist of regional metamorphic rocks.

In pegmatites, associations include quartz, microcline, albite, muscovite, biotite, members of the columbite-tantalite series, cookeite, tourmaline, lepidolite, topaz and spessartine.
In medium-temperature metamorphic deposits beryl is associated with topaz, cassiterite and ferberite-hübnerite.
in Alpine and hydrothermal veins it is found with quartz and feldspar.

Red beryl is found in topaz rhyolites with topaz, high-temperature quartz and bixbyite (Extra Lapis 7.9).

At Tom's quarry, South Australia, beryl occurs intergrown with childrenite, variscite and strontium and iron bearing crandallite (AJM 17.1.28).

At Airy Creek, British Columbia, Canada, aquamarine occurs in a granite pegmatite dyke that cuts high-grade metamorphic gneiss (R&M 85.1.30).

At Lened, Tungsten, Northwest Territories, Canada, emerald occurs in a series of vuggy quartz/carbonate veins within a calc-silicate skarn. The colour is probably due to traces of vanadium (R&M 85.1.28-29).

At the Little Nahanni Pegmatite Group, Tungsten, Northwest Territories, Canada, goshenite occurs within a series of lithium-bearing pegmatites.

At Mountain River, Mackenzie Mountains, Northwest Territories, Canada, emerald occurs in quartz-plagioclase-carbonate veins hosted in shale, siltstone and sandstone. The colour is due to chromium Cr and vanadium V (R&M 84.4.366-367).

At Port Joli, Nova Scotia, Canada, beryl occurs embedded in pegmatite within a biotite granite (R&M 85.1.31).

The Taylor pegmatite, Ontario, Canada, intrudes altered ultramafic rocks, which are the likely source of chromium which causes the green colour of the emerald which is found there (R&M 85.1.28 ).

At the Sapo mine, Minas Gerais, Brazil, beryl occurs in pegmatite associated with quartz, albite and microcline (Min Rec 40.4.288-289).

At Pingwu County, Sichuan, China, beryl is associated with tin and tungsten minerals.

In New York City, USA, beryl crystals are found in pegmatites that cut schist and gneiss, and also frozen in a smoky quartz matrix.

The Consolidated Quarry at Maine, USA, is in a simple granite pegmatite, enriched in lithium in some zones. These have cavities that contain albite, muscovite and beryl, together with other minerals. The paragenesis for the beryl alteration is
beryl → beryllonitemoraesitehydroxylherderitefluorapatitegreifensteinite.
Late-stage low-temperature aqueous fluids likely caused partial dissolution of primary beryl resulting in the formation of hydroxylherderite and other secondary beryllium phosphates (R&M 90.3.275).

At Yucca Valley, California, USA, aquamarine occurs in pockets in pegmatite associated with cleavelandite (variety of albite) and smoky quartz (R&M 87.6.502-508).

In the Sierrita Mountains, Arizona, USA, aquamarine occurs in pegmatites embedded in white quartz enclosed by feldspar, with quartz and mica or in contact with biotite (R&M 88.3.222-230).

At Stoneham, Maine, USA, beryl occurs mostly in solid pegmatites, and only rarely in pockets. When it is in quartz it is aquamarine, but the beryl occurring in feldspar is common beryl (R&M 91.1.28-33).

Alteration

At high temperature and pressure beryl commonly alters to different secondary minerals, depending on the pH.
At pH 2 to 3 (strongly acid) quartz is the dominant alteration product.
At pH 4 to 5 bertrandite, euclase or phenakite are formed.
Near the neutral pH of 7 bertrandite or bavenite are produced.
At pH of 8 to 9 (alkaline) bavenite, milarite or bityite are produced.
At pH 10 to 11 (strongly alkaline) epididymite or eudidymite are produced.
At high temperature and pressure beryl becomes unstable and breaks down into chrysoberyl, phenakite and quartz (Extra Lapis 7.9-10).

bertrandite, euclase and quartz to beryl and H2O
Be4Si2O7(OH)2 + 8BeAlSiO4(OH) + 14SiO2 ⇌ 4Be3Al2Si6O18 + 5H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

bertrandite and kaolinite to euclase, beryl and H2O
4Be4Si2O7(OH)2 + 7Al2Si2O5(OH)4 ⇌ 10BeAlSiO4(OH) + 2Be3Al2Si6O18 + 13H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

bertrandite, kaolinite and quartz to beryl and H2O
3Be4Si2O7(OH)2 + 4Al2Si2O5(OH)4 + 10SiO2 ⇌ 4Be3Al2Si6O18 + 11H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

beryl to chrysoberyl, phenakite and silica (dry)
Be3Al2Si6O18 to BeAl2O4 + Be2(SiO4) + 5SiO2 (dry)
Increasing temperature and pressure favours the forward reaction. At a pressure of 4 kbar the equilibrium temperatute is 1300 deg C (AM 71.277-300).

beryl and aluminium silicate to chrysoberyl and silica (water saturated)
Be3Al2Si6O18Be + 2Ky to 3BeAl2O4 + 8SiO2 (water saturated)
At high pressure, above 8 kbar, the aluminium silicate phase is kyanite. Increasing temperature and decreasing pressure favours the forward reaction. At a pressure of 16 kbar the equilibrium temperature is about 850oC (AM 71.277-300).

euclase to beryl, chrysoberyl, phenakite and H2O
20Eu to 3Be3Al2Si6O18 + 7BeAl2O4 + 2Be2(SiO4) + 10H2O
Increasing temperature and decreasing pressure favours the forward reaction. At a pressure of 6 kbar the equilibrium temperature is about 500oC, in the absence of impurities which might be incorporated in the beryl (AM 71.277-300).

euclase to phenakite, chrysoberyl, beryl and H2O
20BeAlSiO4(OH) ⇌ 2Be2(SiO4) + 7BeAl2O4 + 3Be3Al2Si6O18 + 10H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

euclase and silica to beryl, chrysoberyl and H2O
4Eu + 2SiO2 to Be3Al2Si6O18 + BeAl2O4 + 2H2O
Increasing temperature and decreasing pressure favours the forward reaction. At a pressure of 8 kbar the equilibrium temperature is about 500oC, in the absnece of impurities which might be incorporated in the beryl (AM 71.277-300).

euclase and quartz to beryl, kaolinite and H2O
6BeAlSiO4(OH) + 8SiO2 ⇌ 2Be3Al2Si6O18 + Al2Si2O5(OH)4 + H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

euclase and quartz to chrysoberyl, beryl and H2O
4BeAlSiO4(OH) + 2SiO2 ⇌ BeAl2O4 + Be3Al2Si6O18 + 2H2O
Increasing temperature favours the forward reaction (AM 63.664-676).

Common impurities: Fe,Mn,Mg,Ca,Cr,Na,Li,Cs,O,H,OH,H2O,K,Rb

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