Is euclase a beryl?
Euclase is not beryl, the species of aquamarine and emerald: BeAlSiO4(OH), monoclinic, against hexagonal Be3Al2(Si6O18), and forms where beryl breaks down.
No. Euclase, BeAlSiO4(OH), is monoclinic and biaxial; beryl, Be3Al2(Si6O18), is hexagonal and uniaxial, and the IMA list gives each its own row. They are related: the euclase sheet calls it a product of the decomposition of beryl in pegmatites. Per beryllium atom, beryl carries two silicons and euclase one, and euclase adds hydroxyl.
In short
- Two species, one family tree. The September 2026 IMA-CNMNC Master List lists euclase, BeAlSiO4(OH), G, 1792, Brazil, and beryl, Be3Al2(Si6O18), G, with its year printed as ? and its country as unknown. The Handbook of Mineralogy euclase sheet says it is the product of decomposition of beryl in pegmatites and lists beryl among its associates.
- The silicon-per-beryllium check. Divide each formula by its beryllium. Beryl: 2 Si and 0.67 Al per Be, no hydroxyl. Euclase: 1 Si and 1 Al per Be, plus one OH. Going from beryl to euclase, half the silicon per beryllium goes, aluminium rises by half, and hydroxyl comes in. Bertrandite, which its sheet calls commonly an alteration product of beryl, goes further: 0.5 Si per Be and no aluminium.
- What separates them in the hand. Optics, decisively: euclase biaxial (+) from 1.651, beryl uniaxial (−) to 1.610, a 0.041 gap. Cleavage: perfect on {010} against imperfect on {0001}. Hardness does not (7.5 against 7.5 to 8), and neither does colour: both sheets run from colourless through pale to deep blue and green.
- Documented failure: the balance. A 20.00 g piece reads 13.31 to 13.55 g in water as euclase and 12.40 to 13.27 g as beryl. The 0.045 g between them is smaller than the spread inside either range (0.24 g and 0.87 g), so a weighing near 13.3 g decides little. The International Gem Society euclase article says some aquamarines have been misrepresented as euclase, and that the two have different optical and physical properties.
- Not repeated here. The silicon test on is chrysoberyl a beryl, the two-condition rule on is aquamarine a beryl and the 1.63 refractometer line on is kunzite a beryl each answer their own question. Euclase’s lowest index, 1.651, also sits above that 1.63 line.
| Mineral (IMA formula) | Si per Be | Al per Be | OH | System | Hardness | Density; 20.00 g in water | What the sheet says about beryl |
|---|---|---|---|---|---|---|---|
| Beryl, Be3Al2(Si6O18) | 2 | 0.67 | None | Hexagonal | 7.5–8 | 2.63–2.97; 12.40–13.27 g | — |
| Euclase, BeAlSiO4(OH) | 1 | 1 | 1 per Be | Monoclinic | 7.5 | 2.99–3.10; 13.31–13.55 g | Product of decomposition of beryl in pegmatites; beryl an associate |
| Bertrandite, Be4Si2O7(OH)2 | 0.5 | 0 | 0.5 per Be | Orthorhombic | 6–7 | 2.59–2.60; 12.28–12.31 g | Commonly an alteration product of beryl, more rarely primary |
| Phenakite, Be2(SiO4) | 0.5 | 0 | None | Hexagonal | 7.5–8 | 2.93–3.00; 13.17–13.33 g | Beryl an associate |
| Chrysoberyl, BeAl2O4 | 0 | 2 | None | Orthorhombic | 8.5 | 3.75; 14.67 g | Beryl an associate |
Is euclase a type of beryl?
No: a different species. The September 2026 IMA list gives euclase its own row, BeAlSiO4(OH), status G, 1792, country Brazil, and beryl its own, Be3Al2(Si6O18), status G. The Handbook of Mineralogy euclase sheet calls euclase monoclinic, point group 2/m; the beryl sheet calls beryl hexagonal, 6/m 2/m 2/m. A whole-word scan of the list finds euclase in one line only, its own row; it is not a variety name of anything. The clause-by-clause mineral test is on is quartz a mineral.
But it comes from beryl. The euclase sheet’s Occurrence line is the product of decomposition of beryl in pegmatites, and in low-temperature alpine veins; its associates are feldspar, quartz, topaz, beryl, mica, calcite, ankerite and chlorite. The International Gem Society says the same thing in its own words: euclase can form geologically from the decomposition of beryl and is often found with beryl, but they are distinct mineral species. So a pegmatite piece can carry both. The species page, with its 3.115 cell check, is euclase.
The silicon-per-beryllium check, worked
Method. Take each IMA formula and divide its atoms by the number of beryllium atoms. Beryl, Be3Al2(Si6O18): 6 Si ÷ 3 Be = 2, 2 Al ÷ 3 Be = 0.67, no hydrogen. Euclase, BeAlSiO4(OH): 1, 1 and one hydroxyl. Bertrandite, Be4Si2O7(OH)2: 0.5 Si, no Al, 0.5 OH. Phenakite, Be2(SiO4): 0.5 Si. Chrysoberyl, BeAl2O4: no Si, 2 Al.
What it shows. The two sheets that print themselves as products of beryl, euclase and bertrandite, both carry less silicon per beryllium than beryl and both carry hydroxyl, which beryl’s formula does not. Euclase keeps aluminium; bertrandite loses it. All four non-beryl sheets list beryl among their associates. On standard atomic weights euclase is 6.21% beryllium by mass against beryl’s 5.03%, so the breakdown product is richer in beryllium per gram.
Documented limit. The ratio does not define beryl on its own. Chkalovite, Na2BeSi2O6 on the IMA list, also has 2 Si per Be, and is not a beryl; what makes beryl is the (Si6O18) ring written into its formula. The check says euclase is not beryl; it does not say any mineral with 2 Si per Be is.
How do you tell euclase from aquamarine?
The question people actually face. The International Gem Society says some aquamarines have been misrepresented as euclase, and that the two have different optical and physical properties. Aquamarine is beryl; its own tests are on how to tell if aquamarine is real.
What separates them. Optic class and index first: euclase biaxial (+), α 1.651 to 1.653, γ 1.669 to 1.675; beryl uniaxial (−), ω 1.567 to 1.610. Euclase’s lowest index is 0.041 above beryl’s highest. Cleavage next: euclase perfect on {010}, the cleavage its name is for; beryl imperfect on {0001}. Density only at the margin: 2.99 to 3.10 against 2.63 to 2.97, so 20.00 g reads 13.31 to 13.55 g against 12.40 to 13.27 g, a 0.045 g gap. Method on how to measure specific gravity at home.
What does not. Hardness, 7.5 against 7.5 to 8, and colour: the euclase sheet lists pale green to deep yellowish green, greenish blue and pale blue to deep blue, and the beryl sheet pale blue to sky-blue and bluish green. Scratching a cut stone damages it; see how to test mineral hardness properly.
Is euclase a gemstone, and where is it found?
A gem to the gem society, a pegmatite mineral to the Handbook. The International Gem Society says Brazil produces most cuttable, gem-quality euclase and that radiation treatments can turn colourless euclase green or blue. The Handbook says nothing about cutting or treatment, and no fetched source names another use, so this page states none.
Where. The euclase sheet names the southern Urals, Epprechtstein in Bavaria, Alto Ligonha in Mozambique, Morogoro in Tanzania, Karoi in Zimbabwe, many places in Minas Gerais, and large crystals from the Gachalá mine near Chivor, Colombia. The beryl sheet also names Alto Ligonha and Minas Gerais, and the Chivor district for exceptional green crystals. More classification questions are in the collecting guides. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.