spore: profile id: gemstones-technical spore_version: 0.2 family: optical-crystals name: Technical gemstone minerals (beryl, opal, turquoise, feldspar, olivine) abbreviation: Be3Al2Si6O18 / SiO2 / CuAl6(PO4)4(OH)8 / KAlSi3O8 / (Mg,Fe)2SiO4 role: gem-quality minerals used as hard, transparent or decorative crystal material; beryl is also a beryllium feedstock category: glasses-optics type: optical-crystals summary: | Five gem minerals, grouped because they are sold and studied as crystal or mineral material rather than as single compounds: beryl (emerald is its green chromium-bearing form), opal (amorphous hydrated silica), turquoise (a hydrated copper aluminium phosphate), orthoclase feldspar (the family that includes moonstone) and olivine (peridot is its magnesium-rich form). The Handbook of Mineralogy gives beryl a Mohs hardness of 7.5 to 8 and a measured density of 2.63 to 2.97 g/cm3, with an ordinary refractive index of 1.567 to 1.610. Turquoise is softer, at 5 to 6, and orthoclase is 6 to 6.5. Opal has the lowest density of the set, at 1.9 to 2.3 g/cm3, with a refractive index of 1.43. Goodfellow's search and gemstones pages read in this run list none of these minerals, so this file does not claim that Goodfellow sells them. Values are kept with the source that prints each one. best_for: Hard, transparent mineral material where hardness and density matter (beryl and forsterite are the hardest, at Mohs 7 to 8) weakest_at: 'Brittleness and cleavage: the Handbook lists beryl, orthoclase and forsterite as brittle, and orthoclase cleaves perfectly on two planes. Opal and turquoise are softer, at Mohs 5 to 6' identity: formula: Be3Al2Si6O18 (beryl); CuAl6(PO4)4(OH)8 4H2O (turquoise); SiO2 with water (opal); KAlSi3O8 (orthoclase); (Mg,Fe)2SiO4 (olivine); Mg2SiO4 (forsterite) crystal_system: beryl hexagonal; turquoise triclinic; orthoclase monoclinic; olivine orthorhombic; opal amorphous (no crystals) source: hom-beryl where: Crystal Data row of the beryl, turquoise, orthoclase and forsterite Handbook entries; olivine and opal from the webmineral Olivine and Opal pages (Crystallography sections) tags: environments: [] stresses: [] applications: - structures - electronics-and-chips properties: - benchmark: density label: Density of beryl, measured range value: 2.63 value_high: 2.97 bound: range unit: g/cm3 scope: material conditions: mineral: beryl (Be3Al2Si6O18), including emerald note: Handbook says density increases with alkali content; average 2.7 method: Range printed in the Handbook of Mineralogy beryl entry status: ground source: hom-beryl where: Physical Properties paragraph, D(meas.) value - benchmark: density label: Density of beryl, calculated value: 2.64 unit: g/cm3 scope: material conditions: mineral: beryl (Be3Al2Si6O18) method: Calculated value printed in the Handbook of Mineralogy beryl entry status: calculated source: hom-beryl where: Physical Properties paragraph, D(calc.) value - benchmark: mohs_hardness label: Hardness of beryl value: 7.5 value_high: 8 bound: range unit: '-' scope: material conditions: mineral: beryl (Be3Al2Si6O18) scale: Mohs (the Handbook prints the hardness without naming the scale) method: Range printed in the Handbook of Mineralogy beryl entry status: ground source: hom-beryl where: Physical Properties paragraph, Hardness row - benchmark: refractive_index label: Refractive index of beryl, ordinary ray (omega) value: 1.567 value_high: 1.61 bound: range unit: '-' scope: material conditions: mineral: beryl (Be3Al2Si6O18) wavelength: not stated in the entry note: Handbook says the index increases with alkali content method: Range printed in the Handbook of Mineralogy beryl entry status: ground source: hom-beryl where: Optical Properties paragraph (omega printed as a symbol garbled in the text read) - benchmark: refractive_index label: Refractive index of beryl, extraordinary ray (epsilon) value: 1.565 value_high: 1.599 bound: range unit: '-' scope: material conditions: mineral: beryl (Be3Al2Si6O18) wavelength: not stated in the entry method: Range printed in the Handbook of Mineralogy beryl entry status: ground source: hom-beryl where: Optical Properties paragraph (epsilon printed as a symbol garbled in the text read) - benchmark: density label: Density of turquoise, measured value: 2.86 unit: g/cm3 scope: material conditions: mineral: turquoise (CuAl6(PO4)4(OH)8 4H2O) note: Handbook says less when massive method: Value printed in the Handbook of Mineralogy turquoise entry status: ground source: hom-turquoise where: Physical Properties paragraph, D(meas.) value - benchmark: mohs_hardness label: Hardness of turquoise value: 5 value_high: 6 bound: range unit: '-' scope: material conditions: mineral: turquoise scale: Mohs (the Handbook prints the hardness without naming the scale) method: Range printed in the Handbook of Mineralogy turquoise entry status: ground source: hom-turquoise where: Physical Properties paragraph, Hardness row - benchmark: refractive_index label: Refractive index of turquoise, alpha value: 1.61 unit: '-' scope: material conditions: mineral: turquoise wavelength: not stated in the entry method: Value printed in the Handbook of Mineralogy turquoise entry status: ground source: hom-turquoise where: Optical Properties paragraph, alpha value - benchmark: refractive_index label: Refractive index of turquoise, beta value: 1.62 unit: '-' scope: material conditions: mineral: turquoise wavelength: not stated in the entry method: Value printed in the Handbook of Mineralogy turquoise entry status: ground source: hom-turquoise where: Optical Properties paragraph, beta value - benchmark: refractive_index label: Refractive index of turquoise, gamma value: 1.65 unit: '-' scope: material conditions: mineral: turquoise wavelength: not stated in the entry method: Value printed in the Handbook of Mineralogy turquoise entry status: ground source: hom-turquoise where: Optical Properties paragraph, gamma value - benchmark: density label: Density of opal, range value: 1.9 value_high: 2.3 bound: range unit: g/cm3 scope: material conditions: mineral: opal (SiO2 with water) note: the page gives an average of 2.09 g/cm3 method: Range printed on the webmineral opal page (Physical Properties) status: ground source: webmineral-opal where: Physical Properties of Opal, density range - benchmark: mohs_hardness label: Hardness of opal value: 5.5 value_high: 6 bound: range unit: '-' scope: material conditions: mineral: opal scale: Mohs (the webmineral page compares it to a knife blade and orthoclase) method: Range printed on the webmineral opal page status: ground source: webmineral-opal where: Physical Properties of Opal, Hardness row - benchmark: refractive_index label: Refractive index of opal value: 1.43 unit: '-' scope: material conditions: mineral: opal optical_class: isotropic method: Value printed on the webmineral opal page status: ground source: webmineral-opal where: Optical Properties of Opal, isotropic n value - benchmark: density label: Density of orthoclase, measured range value: 2.55 value_high: 2.63 bound: range unit: g/cm3 scope: material conditions: mineral: orthoclase (KAlSi3O8), the feldspar family that includes moonstone note: moonstone is an adularia variety; the Handbook orthoclase entry does not name moonstone method: Range printed in the Handbook of Mineralogy orthoclase entry status: ground source: hom-orthoclase where: Physical Properties paragraph, D(meas.) value - benchmark: mohs_hardness label: Hardness of orthoclase value: 6 value_high: 6.5 bound: range unit: '-' scope: material conditions: mineral: orthoclase scale: Mohs (the Handbook prints the hardness without naming the scale) method: Range printed in the Handbook of Mineralogy orthoclase entry status: ground source: hom-orthoclase where: Physical Properties paragraph, Hardness row - benchmark: refractive_index label: Refractive index of orthoclase, alpha value: 1.518 value_high: 1.52 bound: range unit: '-' scope: material conditions: mineral: orthoclase wavelength: not stated in the entry method: Range printed in the Handbook of Mineralogy orthoclase entry status: ground source: hom-orthoclase where: Optical Properties paragraph, alpha value - benchmark: refractive_index label: Refractive index of orthoclase, beta value: 1.522 value_high: 1.524 bound: range unit: '-' scope: material conditions: mineral: orthoclase wavelength: not stated in the entry method: Range printed in the Handbook of Mineralogy orthoclase entry status: ground source: hom-orthoclase where: Optical Properties paragraph, beta value - benchmark: refractive_index label: Refractive index of orthoclase, gamma value: 1.522 value_high: 1.525 bound: range unit: '-' scope: material conditions: mineral: orthoclase wavelength: not stated in the entry method: Range printed in the Handbook of Mineralogy orthoclase entry status: ground source: hom-orthoclase where: Optical Properties paragraph, gamma value - benchmark: density label: Specific gravity of olivine, calculated value: 3.3 unit: g/cm3 scope: material conditions: mineral: olivine group, (Mg,Fe)2SiO4 method: Calculated value printed on the webmineral olivine page status: calculated source: webmineral-olivine where: Calculated Properties of Olivine, Specific Gravity note - benchmark: mohs_hardness label: Hardness of olivine value: 6.5 value_high: 7 bound: range unit: '-' scope: material conditions: mineral: olivine group (peridot is a magnesium-rich member) scale: Mohs (the webmineral page compares it to pyrite and quartz) method: Range printed on the webmineral olivine page status: ground source: webmineral-olivine where: Physical Properties of Olivine, Hardness row - benchmark: refractive_index label: Refractive index of olivine, alpha value: 1.63 value_high: 1.65 bound: range unit: '-' scope: material conditions: mineral: olivine group wavelength: not stated on the page method: Range printed on the webmineral olivine page status: ground source: webmineral-olivine where: Optical Properties of Olivine, Optical Data row (a) - benchmark: refractive_index label: Refractive index of olivine, gamma value: 1.67 value_high: 1.69 bound: range unit: '-' scope: material conditions: mineral: olivine group wavelength: not stated on the page method: Range printed on the webmineral olivine page status: ground source: webmineral-olivine where: Optical Properties of Olivine, Optical Data row (g) - benchmark: density label: Density of forsterite, measured value: 3.275 unit: g/cm3 scope: material conditions: mineral: forsterite (Mg2SiO4), the magnesium end member of the olivine series method: Value printed in the Handbook of Mineralogy forsterite entry status: ground source: hom-forsterite where: Physical Properties paragraph, D(meas.) value - benchmark: mohs_hardness label: Hardness of forsterite value: 7 unit: '-' scope: material conditions: mineral: forsterite scale: Mohs (the Handbook prints the hardness without naming the scale) method: Value printed in the Handbook of Mineralogy forsterite entry status: ground source: hom-forsterite where: Physical Properties paragraph, Hardness row - benchmark: refractive_index label: Refractive index of forsterite, gamma value: 1.67 unit: '-' scope: material conditions: mineral: forsterite wavelength: not stated in the entry method: Value printed in the Handbook of Mineralogy forsterite entry status: ground source: hom-forsterite where: Optical Properties paragraph, gamma value corrosion: [] risks: hazards: - text: USGS says beryllium is toxic, and that industry must control beryllium dust, fumes and mists in the workplace. Beryl is an imported beryllium feedstock, so it carries the same concern. ghs: [] source: usgs-beryllium-2026 where: Events, Trends, and Issues paragraph failure_risks: - mode: Brittle fracture trigger: Impact or bending of a faceted or thin piece consequence: The Handbook lists beryl, orthoclase and forsterite as brittle, so these crystals break rather than bend. severity: moderate source: hom-beryl where: Physical Properties paragraph, Tenacity row - mode: Perfect cleavage in orthoclase trigger: Stress along the cleavage planes consequence: The Handbook gives perfect cleavage on the 001 and 010 planes, so the crystal splits along flat faces. severity: moderate source: hom-orthoclase where: Physical Properties paragraph, Cleavage row side_effects: [] handling: - text: Keep beryl dust, fumes and mists out of the workplace air, as the USGS notes that industry must control beryllium dust. source: usgs-beryllium-2026 where: Events, Trends, and Issues paragraph mitigations: [] uses: - application: electronics-and-chips device: Beryllium metal, oxide and beryllium-copper master alloy made from beryllium hydroxide (Utah plant) example: 'USGS: consumer electronics took about 29% of beryllium product sales and semiconductor applications about 2%. Imported beryl was one feedstock for the beryllium hydroxide.' source: usgs-beryllium-2026 where: Domestic Production and Use paragraph - application: structures device: Plate glass, ceramic tiles and sanitaryware, made with feldspar as a flux and raw material example: 'USGS: feldspar is ground for glassmaking and for ceramics, where it works as a flux. Ceramics and pottery took 53% of domestic feldspar end use.' source: usgs-feldspar-2026 where: Domestic Production and Use paragraph; Events, Trends, and Issues paragraph supply: - subject: Beryllium, world mine production 2025 estimate (metric tons of beryllium content) producers: - country: United States share_percent: 53.5 year: 2025 - country: Brazil share_percent: 18.6 year: 2025 - country: China share_percent: 17.9 year: 2025 - country: Nigeria share_percent: 9.3 year: 2025 critical_lists: [] recycling: 'USGS: recovered from new and old scrap, which may be 20% to 25% of total beryllium consumption.' substitutes: - 'USGS: aluminum, silicon carbide, steel or titanium may replace beryllium metal in some uses, but the substitutes reduce performance.' - 'USGS: aluminum nitride or boron nitride may be substituted for beryllium oxide.' source: usgs-beryllium-2026 where: World Mine Production and Reserves table, 2025e column (United States 230 tons, world total 430 rounded). Shares calculated by Space Mushroom as country value divided by the printed world total of 430 (rounded). The rows sum to 432, so the shares are approximate. - subject: Feldspar, world mine production 2025 (thousand metric tons) producers: - country: India share_percent: 19.4 year: 2025 - country: Turkey share_percent: 17.1 year: 2025 - country: Iran share_percent: 12.6 year: 2025 - country: China share_percent: 11.9 year: 2025 critical_lists: [] recycling: 'USGS: feldspar is not recycled by producers; container cullet reduces consumption of feldspar in glass.' substitutes: - 'USGS: imported nepheline syenite was the major alternative material for feldspar.' source: usgs-feldspar-2026 where: World Mine Production and Reserves table, 2025 column. Shares calculated by Space Mushroom as country value divided by the printed world total of 31,000 thousand t (rounded). The rows do not sum exactly to the total. documents: - title: 'Handbook of Mineralogy: Beryl (Mineral Data Publishing, 2001 to 2005 version)' type: database url: https://handbookofmineralogy.org/pdfs/beryl.pdf year: 2001 - title: 'Handbook of Mineralogy: Turquoise (Mineral Data Publishing)' type: database url: https://handbookofmineralogy.org/pdfs/turquoise.pdf year: 2005 - title: 'Handbook of Mineralogy: Orthoclase (Mineral Data Publishing)' type: database url: https://handbookofmineralogy.org/pdfs/orthoclase.pdf year: 2001 - title: 'Handbook of Mineralogy: Forsterite (Mineral Data Publishing)' type: database url: https://handbookofmineralogy.org/pdfs/forsterite.pdf year: 2001 - title: 'USGS Mineral Commodity Summaries 2026: Beryllium' type: report url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-beryllium.pdf year: 2026 - title: 'USGS Mineral Commodity Summaries 2026: Feldspar and nepheline syenite' type: report url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-feldspar.pdf year: 2026 gaps: - 'Goodfellow: the search pages for beryl, emerald, opal, turquoise, moonstone, feldspar, peridot and olivine, and the Goodfellow gemstones category page, read in this run list none of these minerals. No Goodfellow product code, purity or form is given here, and the file does not claim Goodfellow sells them.' - 'Emerald: the beryl entry covers beryl, and emerald is its green chromium-bearing form. No emerald-specific value (colour, inclusions, chromium content) was read from a source in this run.' - 'Moonstone: no source read names moonstone. The orthoclase values are used as a proxy for the feldspar family. Moonstone''s sheen (adularia) and its own density and index were not sourced.' - 'Peridot: the forsterite values are the magnesium end member. The olivine range from webmineral is a group range. Peridot''s own composition, density and index were not sourced.' - 'Opal: the webmineral page gives density, hardness and index. No water content, dehydration or ageing data for opal was read.' - 'Corrosion or ageing: no corrosion, weathering or ageing source was read for any of the five minerals. The corrosion section is empty for that reason.' - 'Abrasive and substrate uses: no source read in this run names an abrasive or substrate use for beryl, opal, turquoise, feldspar or olivine. Sapphire and ruby are alumina crystals with their own profiles (sapphire.yaml and ruby.yaml); no values from them are reused here.' - Critical-mineral status for beryllium and feldspar was not checked against the USGS critical minerals list in this run. - 'Refractive indices: the Handbook and webmineral pages do not give a wavelength, so the wavelength in conditions is marked as not stated.' - 'Hardness: the Handbook and webmineral pages print hardness without naming the scale. Mohs is assumed for the values as printed.' - Fracture toughness, thermal conductivity and thermal expansion for these five minerals were not found in the sources opened. - The webmineral pages are a secondary database. The olivine and opal values were not checked against a primary paper. sources: hom-beryl: title: 'Handbook of Mineralogy: Beryl (Mineral Data Publishing)' id: Handbook of Mineralogy beryl data sheet, PDF url: https://handbookofmineralogy.org/pdfs/beryl.pdf year: 2001 kind: handbook license: Mineral Data Publishing, all rights reserved; linked, not reproduced hom-turquoise: title: 'Handbook of Mineralogy: Turquoise (Mineral Data Publishing)' id: Handbook of Mineralogy turquoise data sheet, PDF url: https://handbookofmineralogy.org/pdfs/turquoise.pdf year: 2005 kind: handbook license: Mineral Data Publishing, all rights reserved; linked, not reproduced hom-orthoclase: title: 'Handbook of Mineralogy: Orthoclase (Mineral Data Publishing)' id: Handbook of Mineralogy orthoclase data sheet, PDF url: https://handbookofmineralogy.org/pdfs/orthoclase.pdf year: 2001 kind: handbook license: Mineral Data Publishing, all rights reserved; linked, not reproduced hom-forsterite: title: 'Handbook of Mineralogy: Forsterite (Mineral Data Publishing)' id: Handbook of Mineralogy forsterite data sheet, PDF url: https://handbookofmineralogy.org/pdfs/forsterite.pdf year: 2001 kind: handbook license: Mineral Data Publishing, all rights reserved; linked, not reproduced webmineral-olivine: title: 'webmineral: Olivine data page' id: webmineral.com/data/Olivine.shtml (page undated) url: https://webmineral.com/data/Olivine.shtml year: 2026 kind: web license: secondary database page, linked not reproduced webmineral-opal: title: 'webmineral: Opal data page' id: webmineral.com/data/Opal.shtml (page undated) url: https://webmineral.com/data/Opal.shtml year: 2026 kind: web license: secondary database page, linked not reproduced usgs-beryllium-2026: title: 'USGS Mineral Commodity Summaries 2026: Beryllium' id: USGS MCS 2026, beryllium chapter url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-beryllium.pdf year: 2026 kind: report license: public domain (USGS) usgs-feldspar-2026: title: 'USGS Mineral Commodity Summaries 2026: Feldspar and nepheline syenite' id: USGS MCS 2026, feldspar chapter url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-feldspar.pdf year: 2026 kind: report license: public domain (USGS) goodfellow-gemstones: title: 'Goodfellow: Gemstones category page and product search (beryl, emerald, opal, turquoise, feldspar, olivine searches)' id: goodfellow.com/usa/material/gemstones and goodfellow.com/search url: https://www.goodfellow.com/usa/material/gemstones year: 2026 kind: web license: supplier page, linked not reproduced license: CC-BY-4.0 updated: '2026-10-26' review: status: draft method: assistant checked_values: 27 unreachable: 0 caveats: 6 note: Written by an AI assistant on 2026-10-26 from pages and PDFs read in the same run. Goodfellow lists none of these minerals, so the file does not say it sells them. The olivine and opal values come from a secondary database. Moonstone and emerald are covered only through their parent minerals. The hardness scale is not named in the sources and is read as Mohs. No corrosion or ageing source was read. story: recipe: line: The five minerals are not one compound. Beryl is a beryllium aluminium silicate, turquoise a hydrated copper aluminium phosphate, opal a hydrated silica, orthoclase a potassium aluminium silicate, and olivine a magnesium iron silicate. Each is a natural mineral, so the formula varies with the locality. parts: - name: Beryllium symbol: Be role: The light metal in beryl and the source of beryllium metal and oxide. - name: Aluminium symbol: Al role: Present in beryl, turquoise and orthoclase. - name: Silicon symbol: Si role: The main framework element of beryl, opal, orthoclase and olivine. - name: Oxygen symbol: O role: Present in every silicate and phosphate. - name: Copper symbol: Cu role: The colour-giving metal in turquoise. - name: Magnesium and iron symbol: Mg and Fe role: The two cations that form the olivine series; peridot is the magnesium-rich end. risk_groups: - title: For people level: 1 verdict: Beryl carries beryllium toxicity risk lead: USGS says beryllium is toxic and that industry must control its dust, fumes and mists. Beryl is a beryllium feedstock, so the same concern applies to beryl dust. points: - label: Beryllium line: 'USGS: beryllium is toxic, so workplace dust, fumes and mists must be controlled.' - label: Silica line: Opal is a hydrated silica. No silica hazard was read in a source, so none is stated here. - title: If it fails lead: The failure facts come from the Handbook of Mineralogy entries, not from field incidents. points: - label: Breaking line: The Handbook lists beryl, orthoclase and forsterite as brittle, so they break rather than bend. - label: Cleavage line: Orthoclase cleaves perfectly on two planes, so a stressed crystal can split along flat faces. - title: Handling and storage gap: No storage temperature or humidity limit was read for any of the five minerals. points: - label: Dust line: Keep beryl dust out of the air in the workplace, as the USGS says for beryllium. why: These five minerals are the gem minerals that a technical buyer would weigh for hardness, density and optical index. Beryl is the hardest at Mohs 7.5 to 8. Opal is the lightest, with a density of 1.9 to 2.3 g/cm3. Turquoise and opal are the softest, at Mohs 5 to 6. The Handbook and webmineral pages give the index for each mineral, and the USGS covers beryllium and feldspar supply. uses: - where: Beryllium from beryl line: 'USGS: beryllium products went mainly to consumer electronics (about 29%) and aerospace and defense (about 24%). Imported beryl was one feedstock for the beryllium hydroxide used to make metal and oxide.' - where: Feldspar for glass and ceramics line: 'USGS: feldspar is a flux for plate glass, ceramic tiles and sanitaryware. Ceramics and pottery took 53% of domestic feldspar end use.' can_do: - label: Hardness value: 7.5 to 8 line: Beryl is at Mohs 7.5 to 8 in the Handbook of Mineralogy, the hardest of the five. Orthoclase is 6 to 6.5, and turquoise is 5 to 6. - label: Density value: 2.63 to 2.97 g/cm3 line: Measured beryl density is 2.63 to 2.97 g/cm3. Opal is 1.9 to 2.3 g/cm3, and forsterite is 3.275 g/cm3. - label: Refractive index value: 1.567 to 1.610 line: The ordinary refractive index of beryl is 1.567 to 1.610, and opal is isotropic at 1.43. - label: Beryllium supply value: 430 t line: World beryllium mine production was about 430 metric tons of beryllium content in 2025, with the United States at 230 tons. compare: On the printed values, beryl is the hardest of the five minerals at Mohs 7.5 to 8, and forsterite (the magnesium end of the olivine series) is next at Mohs 7. Opal is the lightest, at 1.9 to 2.3 g/cm3. Beryl (2.63 to 2.97 g/cm3) is lighter than the olivine group (3.3) and forsterite (3.275), and turquoise (2.86) falls inside its range. Turquoise and opal are the softest. The sources read give no cost, availability or purity comparison between the minerals as crystal material, and none of them is sold by Goodfellow in the pages read. compare_rows: - label: Hardness benchmark: mohs_hardness - label: Density benchmark: density - label: Refractive index benchmark: refractive_index handling: - Beryl is a beryllium mineral, so control dust and fumes from cutting or grinding, as the USGS says for beryllium. - Orthoclase cleaves on two planes, so support faceted or thin pieces to avoid splitting along a cleavage. - Turquoise and opal are softer than beryl, at Mohs 5 to 6, so avoid abrasive contact. good_for: - 'Hard, transparent mineral material where hardness matters: beryl at Mohs 7.5 to 8, and forsterite at Mohs 7.' - 'Beryllium feedstock: imported beryl converted to beryllium hydroxide, as the USGS describes.' - 'Glass and ceramic raw material: feldspar as a flux for plate glass and ceramic tiles.' watch_out: - 'Brittleness: beryl, orthoclase and forsterite are brittle, and orthoclase has perfect cleavage.' - 'Softness: turquoise and opal are at Mohs 5 to 6, below beryl and orthoclase.' - 'Beryllium toxicity: beryl dust must be controlled.' - 'Source limits: no corrosion, ageing, fracture toughness or thermal data was read for these minerals.' verdict: Beryl is the hardest and most useful for technical crystal work, with a clear beryllium-toxicity limit. Opal, turquoise and the feldspar and olivine minerals are useful as data points but have few technical uses in the sources read. Goodfellow does not list these minerals on the pages read in this run, so this file is a mineral data record, not a supplier listing. For the alumina crystals used as optics and substrates, see the sapphire and ruby profiles (sapphire.yaml and ruby.yaml).