Bertrandite
Bertrandite, Be4Si2O7(OH)2: orthorhombic, hardness 6 to 7, density 2.59 to 2.60, 15.13% beryllium. The one-water check, Spor Mountain arithmetic and localities.
Bertrandite is a beryllium silicate hydroxide, Be4Si2O7(OH)2 on the IMA list (G, 1878, France): orthorhombic, colourless to slightly yellow, with heart-shaped twins, hardness 6 to 7, density 2.59 to 2.60, 15.13% beryllium. USGS calls it the source mineral for more than 90 per cent of the world’s beryllium, mined at Spor Mountain, Utah.
In short
- The species. The Handbook of Mineralogy sheet gives an orthorhombic beryllium silicate, point group mm2, in thin tabular to needlelike crystals to 5 cm and radial aggregates, with common heart-shaped or V-shaped twins; cleavage perfect on {001}; hardness 6 to 7; density 2.59 to 2.60; colourless to slightly yellow; biaxial (−); pyroelectric. Commonly an alteration product of beryl, more rarely primary. The September 2026 IMA-CNMNC Master List writes Be4Si2O7(OH)2, status G, 1878, France.
- The one-water check. Bertrandite’s formula is exactly two phenakite formulas plus one water: 2 Be2SiO4 + H2O = Be4Si2O9H2, written Be4Si2O7(OH)2, and 2 × 110.11 + 18.02 = 238.23. The USGS Professional Paper 1802-E says phenakite is stable above 250 °C and hydrates to bertrandite at lower temperatures (Barton, 1986). Worked, bertrandite is 15.13% beryllium, 42.00% BeO and 7.56% H2O, the sheet’s ideal column; its cell gives a density of 2.604 against the printed [2.61].
- The Spor Mountain arithmetic. USGS reports proven bertrandite reserves at Spor Mountain of 5.75 million dry tons at an average grade of 0.265 per cent beryllium. Worked: 2.65 kg of beryllium per tonne, and 5.75 million × 0.265% = 15,238 t, matching USGS’s about 15,200 metric tons. The beryllium in a tonne of that ore is the beryllium of 17.5 kg of ideal bertrandite.
- Documented failure: the two USGS figures do not reconcile. On the ideal formula, a grade of 0.265% beryllium needs 1.75% bertrandite in the ore. The same USGS chapter says the Spor Mountain ore contains about 1 per cent or less bertrandite, and that the Spor Mountain variety has properties intermediate between colloidal bertrandite and bertrandite proper. It does not reconcile the two numbers, and this page offers no reason.
- Where. The sheet names the Barbin quarries at Petit-Port near Nantes, France; Val Vigezzo, Italy; Písek, Czech Republic; the Strickland quarry, Portland, Connecticut; Amelia, Virginia; Mt. Antero, Colorado; Spor Mountain, Utah, a large commercial deposit; the Pala district, California; Sierra de Aguachile, Coahuila, Mexico; the Golconda mine, Minas Gerais; Klein Spitzkopje, Namibia; the Tae Hwa mine, South Korea; and Akchatau, Kara-Oba and Kounrad, Kazakhstan.
| Mineral | IMA formula | IMA status, year, country | Be per Si | Formula mass | Be by mass | System (sheet) | Hardness (sheet) | D(meas.); 20.00 g in water |
|---|---|---|---|---|---|---|---|---|
| Bertrandite | Be4Si2O7(OH)2 | G, 1878, France | 2.00 | 238.23 | 15.13% | Orthorhombic | 6–7 | 2.59–2.60; 12.28–12.31 g |
| Phenakite | Be2(SiO4) | G, 1833, Russia | 2.00 | 110.11 | 16.37% | Hexagonal | 7.5–8 | 2.93–3.00; 13.17–13.33 g |
| Sphaerobertrandite | Be3(SiO4)(OH)2 | Rd, 2003 s.p., Russia / Norway | 3.00 | 153.13 | 17.66% | Sheet not read | — | — |
| Beryllite | Be3(SiO4)(OH)2·H2O | G, 1954, Russia | 3.00 | 171.15 | 15.80% | Sheet not read | — | — |
| Beryl (comparator, has Al) | Be3Al2(Si6O18) | G, ?, unknown | 0.50 | 537.49 | 5.03% | Hexagonal | 7.5–8 | 2.63–2.97; 12.40–13.27 g |
What is bertrandite? Beryllium silicate hydroxide
Bertrandite is a beryllium silicate with hydroxyl, and its sheet calls it commonly an alteration product of beryl, more rarely a primary mineral. The Handbook of Mineralogy bertrandite sheet places it in fissures in granites and associated pegmatites and in miarolitic cavities in greisens, with beryl, phenakite, herderite, tourmaline, muscovite, fluorite and quartz. It is orthorhombic, point group mm2, space group Cmc21, a 8.7135, b 15.268, c 4.5683 Å, Z 4. Crystals are thin tabular, commonly prismatic to needlelike, to 5 cm, in radial aggregates. Twinning is common on {011} or {021}, giving heart-shaped or V-shaped twins whose axes cross at about 60° and 120°.
Physical and optical properties. Cleavage perfect on {001}; distinct on {100}, {010} and {110}. Hardness 6 to 7; measured density 2.59 to 2.60, calculated [2.61]; pyroelectric. Transparent; colourless to slightly yellow; vitreous, pearly on {001}. Biaxial (−), α 1.583 to 1.591, β 1.598 to 1.605, γ 1.608 to 1.614, 2V about 75°, dispersion r < v, weak. A ligature-aware search of the sheet finds no fluorescence line; it prints none.
Name. For Emile Bertrand (1844–1909), French mineralogist. Type material is at the National School of Mines, Paris; the IMA list gives 1878 and France. The sheet marks no type locality; see what is a type locality.
Bertrandite and phenakite: the one-water check
Bertrandite is phenakite plus water, atom for atom: two Be2SiO4 and one H2O make Be4Si2O7(OH)2. Count it: 4 Be, 2 Si, 8 + 1 = 9 O and 2 H on both sides. The formula masses agree, 2 × 110.11 + 18.02 = 238.23. Both carry 2.00 beryllium per silicon; only the water differs. The USGS Professional Paper 1802-E, Beryllium (Foley and others, 2017) says bertrandite is the stable mineral in surface environments, forming at or below 250 °C, that phenakite is stable above 250 °C, and that phenakite hydrates to bertrandite at lower temperatures, citing Barton (1986). The bertrandite sheet lists phenakite as an associate, and the two sheets share three named localities: Mt. Antero, Colorado; Amelia, Virginia; and Klein Spitzkopje, Namibia.
The composition, worked. On standard atomic weights bertrandite is 15.13% beryllium, 42.00% BeO, 50.44% SiO2 and 7.56% H2O, the sheet’s ideal column (2) exactly; USGS’s Table E2 gives 42 per cent BeO. The cell volume, 8.7135 × 15.268 × 4.5683 = 607.76 Å3, holds four formula units for a density of 2.604, against the sheet’s bracketed [2.61] and measured 2.59 to 2.60. A 20.00 g piece reads 12.28 to 12.31 g in water; see how to measure specific gravity at home.
The Barbin analysis. The sheet’s column (1), from Barbin, France, reads SiO2 49.26, BeO 42.0, Fe2O3 1.40, H2O 6.90, Al2O3 trace, total 99.56. Per two silicon that is 4.10 beryllium, against 4, and 0.93 H2O, against 1. Of the four Be–Si–O–H rows on the IMA list, in the table above, bertrandite has the least beryllium by mass, 15.13%, and sphaerobertrandite the most, 17.66%. Beryl, with aluminium, has 5.03%; the beryl-to-bertrandite relation in atoms per beryllium is set out on is euclase a beryl.
Is bertrandite an ore of beryllium? What USGS says
Yes, per USGS: bertrandite is the source mineral for more than 90 per cent of beryllium produced globally. The USGS Professional Paper 1802-E, Beryllium (Foley and others, 2017) says the current sole domestic source of beryllium is bertrandite ore from the Spor Mountain deposit in Utah, and that bertrandite and phenakite are the predominant ore minerals in near-surface volcanogenic and carbonate-hosted deposits, while beryl is the main beryllium ore mineral in plutonic and metamorphic settings. It adds that ultra-high-purity beryllium is made exclusively from beryl, as beryl typically has fewer impurities, such as fluorine and uranium, than bertrandite. The USGS Mineral Commodity Summaries 2025, Beryllium says one company in Utah mined bertrandite ore and converted it, with imported beryl, into beryllium hydroxide.
The Spor Mountain arithmetic. USGS gives Materion’s reported proven reserves at year-end 2011 as 5.75 million dry tons at an average grade of 0.265 per cent beryllium, about 0.8 per cent BeO, containing about 15,200 metric tons of beryllium. Worked: 5.75 million × 0.265% = 15,238 t, and 0.265% beryllium is 0.735% BeO by mass, which the chapter rounds to about 0.8. A tonne of ore holds 2.65 kg of beryllium, as much as 17.5 kg of ideal bertrandite. The sheet’s own Distribution line calls Spor Mountain, Juab Co., a large commercial deposit.
Documented failure. On the ideal formula a 0.265% grade means 1.75% bertrandite in the ore, yet the same chapter says the ore contains about 1 per cent or less bertrandite, and the 0.23% cutoff grade it quotes would already need 1.52%. The chapter also says Spor Mountain bertrandite has properties intermediate between colloidal bertrandite and bertrandite proper, but it does not tie that to the grade, and this page does not either. The Mineral Commodity Summaries footnote that bases production on 4% beryllium content of bertrandite and beryl sources is a figure for the sources, not for either mineral: worked, pure bertrandite is 15.13% and pure beryl 5.03%. Uses of the metal are USGS’s subject, not a property of the specimen. Beryllium-bearing dust is a hazard question this page does not answer; it is routed to toxic minerals in a collection, and nothing here is advice.
Where is bertrandite found? The sheet’s localities
The sheet says it occurs in small amounts at numerous localities, and names a few affording pure material or larger crystals. In France, near Nantes, in the Barbin quarries at Petit-Port, Loire-Atlantique. Val Vigezzo, Piedmont, Italy. Písek, Czech Republic. In the USA, the Strickland quarry, Portland, Middlesex Co., Connecticut; Amelia, Virginia; Mt. Antero, Chaffee Co., Colorado and elsewhere; Spor Mountain, Juab Co., Utah, a large commercial deposit; the Pala district, San Diego Co., California. A large deposit at Sierra de Aguachile, Acuña, Coahuila, Mexico. Large crystals at the Golconda mine, near Governador Valadares, Minas Gerais, Brazil. Klein Spitzkopje, Namibia. The Tae Hwa mine, Chung Cheong Buk Do, South Korea. Akchatau, Kara-Oba and Kounrad, Kazakhstan. The sheet names no British locality.
Reading a label. The sheet gives it as colourless to slightly yellow, in small amounts. On the sheets, density separates it from its common associates: 12.28 to 12.31 g in water for 20.00 g against 12.40 to 13.27 g for beryl and 13.17 to 13.33 g for phenakite. The phenakite and beryl pages carry those sheets in full, and euclase is the other beryl alteration product. The reference section continues at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.