Pyrope
Pyrope, Mg3Al2(SiO4)3, is the magnesium garnet: cubic, hardness 7 to 7.5, density 3.582, index 1.714. Old ruby labels decoded from the IMA garnet report.
Pyrope is the magnesium aluminium garnet, Mg3Al2(SiO4)3: cubic, hardness 7 to 7.5, density 3.582, one refractive index of 1.714, purple-red to deep red. Old labels often call it ruby: of 33 names containing ruby or rubin in the 2013 IMA garnet report’s name list, 14 decode to pyrope, among them Bohemian, Cape and Arizona ruby.
In short
- One species of a large group. The September 2026 IMA-CNMNC Master List lists pyrope as Mg3Al2(SiO4)3, grandfathered, 1803, Czech Republic. The Handbook of Mineralogy sheet places it in the garnet group, in series with almandine and with knorringite. Grew et al., American Mineralogist 98 (2013) give the type locality as Bohemia, the first recognition to Agricola in 1546 and the name to Werner in 1800.
- The ruby-name decoder. Appendix 2 of Grew et al. lists 715 old and trade names for garnets. By script, 33 contain ruby, rubin or rubies: 14 decode to pyrope, 15 to garnet without a species, 3 to almandine and 1 to pyrope-almandine. Bohemian, Cape, Arizona, Colorado, Elie and South African ruby are all pyrope; American and Adelaide ruby are almandine.
- Bohemian garnet, read three ways. Grew et al. decode Bohemian garnet as pyrope-almandine and Bohemian ruby as pyrope. The International Gem Society says the so-called Bohemian garnets, from near Třebenice, are pyropes, and its list of misleading names gives Bohemian ruby as pyrope or rose quartz. The sheet’s Distribution names Mĕrunice (Meronitz), Czech Republic.
- The end-member gap. The sheet’s Dora-Maira analysis is 97.6% magnesium on the garnet’s X site, worked, close to the International Gem Society’s 98% for that locality; the same source puts the purest gem pyrope at about 83%. So the sheet’s 1.714 and 3.582 describe near-pure pyrope, and a gem sold as pyrope reads 1.73 to 1.766, SG 3.65 to 3.87.
- Not separable from spinel by weight. A 20.00 g pyrope reads 14.42 g in water; red spinel reads 14.41 to 14.44 g. Crystal form decides on a crystal: dodecahedra or trapezohedra against octahedra.
| Name on an old label | Grew et al. 2013, Appendix 2 | Second source | IMA row for the name? | Decoded species on its sheet: index; 20.00 g in water |
|---|---|---|---|---|
| Bohemian ruby; Böhmischer rubin | Pyrope | IGS list: pyrope or rose quartz | No | Pyrope: 1.714; 14.42 g |
| Bohemian garnet; Böhmischer granat | Pyrope-almandine | IGS pyrope article: the Bohemian garnets of Třebenice are pyropes | No | Pyrope 1.714, 14.42 g; almandine 1.830, 15.37 g |
| Cape ruby; Cape garnet | Pyrope | IGS list: Cape-ruby, pyrope | No | Pyrope: 1.714; 14.42 g |
| Arizona ruby; anthill garnet | Pyrope | IGS list: Arizona ruby, pyrope. IGS article: chrome pyropes from Arizona are called anthill garnets | No | Pyrope: 1.714; 14.42 g |
| Colorado, Elie, Rocky Mountain, South African ruby | Pyrope | Not on the IGS list | No | Pyrope: 1.714; 14.42 g |
| Chrome pyrope | Pyrope; Cr-pyrope and chromium pyrope: pyrope or knorringite | IGS article: chrome pyrope, from Arizona and Tanzania | No | Knorringite: 1.803; 14.68 g |
| Chrome garnet | Two entries: pyrope (Chapman 1843) and uvarovite (Egleston 1892) | Not on the IGS list | No | Uvarovite: 1.865; 14.69 to 14.75 g |
| American ruby; Adelaide ruby | Almandine | IGS list: American ruby, pyrope or almandite or rose quartz; Adelaide ruby, almandite | No | Almandine: 1.830; 15.37 g |
| Arizona spinel | Almandine | IGS list: red or green garnet | No | Almandine: 1.830; 15.37 g |
| Pyrope | Pyrope | IGS: pyrope | Yes: Mg3Al2(SiO4)3, G, 1803 | 1.714; 14.42 g |
What is pyrope? The magnesium garnet
The names. The September 2026 IMA-CNMNC Master List gives pyrope as Mg3Al2(SiO4)3, status G, 1803, with the Czech Republic as the country of first description. Grew et al., American Mineralogist 98 (2013) write the end-member as {Mg3}[Al2](Si3)O12, give the type locality as Bohemia (Czech Republic), and say pyrope was recognised by Georgius Agricola in 1546 but named by A. G. Werner in 1800; both dates are printed because the two sources differ. The sheet derives the name from the Greek for fire-like, for its fire-red colour.
The composition, worked. On standard atomic weights the formula mass is 403.12, and pyrope is 29.99% MgO, 25.29% Al2O3 and 44.71% SiO2; the sheet’s ideal column prints 30.00, 25.29 and 44.71. Its Dora-Maira massif, Italy analysis, by microprobe, corresponds to (Mg2.87Fe0.05Ca0.02)Al2.01Si3.02O12: magnesium is 97.6% of the X site. An aluminium garnet is named for the dominant X-site cation, the rule worked on the spessartine and almandine pages and not repeated here.
What it looks like, per the sheet. Cubic, point group 4/m -3 2/m; subhedral to euhedral crystals showing the dodecahedron or trapezohedral forms, to 20 cm; also granular and massive. Fracture conchoidal, brittle, hardness 7 to 7.5, density 3.582 measured. Purple-red, pinkish red, red-orange, deep red to almost black; some examples are bluish green in daylight and wine-red in artificial light. Streak white; vitreous; isotropic, n = 1.714. No luminescence line is printed, by a ligature-aware search, and the International Gem Society lists its luminescence as none.
Bohemian ruby, Cape ruby, Arizona ruby: the ruby-name decoder
The ruby-name decoder: in the 2013 IMA garnet report’s list of old and trade names, 14 of the 33 names containing ruby, rubin or rubies decode to pyrope, and none of the 33 decodes to corundum. Grew et al.’s Appendix 2 is a list of synonyms, obsolete, varietal and discredited names for garnet-supergroup minerals, n = 715. Method: the PDF was parsed by word position into name and species columns, the names containing rub were counted, the count was repeated word by word, and each entry was read from the rendered page. The 33 split 14 pyrope, 15 garnet without a species, 3 almandine and 1 pyrope-almandine.
The 14 pyrope names: Arizona rubin, Arizona ruby, Bohemian ruby, Böhmischer rubin, Cape ruby, caprubin, Colorado ruby, Elie ruby, Ely ruby, fashoda ruby, kaprubin, Kolorado-rubin, Rocky Mountain ruby and South African ruby. The three almandine names are Adelaide ruby, alabandine ruby and American ruby; felsinrubin is pyrope-almandine. The garnet-only names include California ruby, Montana ruby, Ceylon ruby and false ruby, where the list does not name a species.
Where the decoder fails, documented. The authors call the list necessarily incomplete and say they did not compile other meanings of the same names. Chrome garnet appears twice, as pyrope after Chapman (1843) and as uvarovite after Egleston (1892); Cr-pyrope and chromium pyrope decode to pyrope or knorringite. The International Gem Society’s list, from Schumann, gives Bohemian ruby as pyrope or rose quartz and American ruby as pyrope, almandite or rose quartz. An old name says what a dealer called the stone, not what it is: an index of 1.714 to the 1.76s and one reading, on the how to tell if garnet is real page, is the test.
Is Bohemian garnet pyrope? Three sources
Bohemian garnet is pyrope in trade use, and pyrope-almandine in the 2013 name list. Grew et al. decode Bohemian garnet and Böhmischer granat as pyrope-almandine, after Werner, and Bohemian ruby, Böhmischer rubin and granati Bohemici as pyrope. The International Gem Society pyrope article says the area near Třebenice (Trebnitz), Czech Republic, produces the best-known pyropes, the so-called Bohemian garnets, in volcanic breccia, tuffs and conglomerates.
What the sheet adds. The pyrope sheet’s Distribution opens with gem material from around Mĕrunice (Meronitz), Czech Republic. It does not use the word Bohemian, and this page does not equate Mĕrunice with Třebenice. The IMA list’s country for pyrope is the Czech Republic, and Grew et al.’s type locality is Bohemia.
Why a mixed name is plausible. The sheet records that pyrope forms a series with almandine, and the International Gem Society says pyropes always contain some almandine and spessartite components and that common dark red garnets are a mixture of almandine and pyrope. A label reading Bohemian garnet names a source and a trade, not a measured composition.
Chrome pyrope, knorringite and colour-change pyrope
Chrome pyrope is pyrope with chromium, and towards the chromium end it becomes knorringite. The pyrope sheet says it forms a series with knorringite. The knorringite sheet gives Mg3Cr2(SiO4)3 (IMA: A, 1968-010, Lesotho), garnet group, bluish green to greenish, n = 1.803 and measured density 3.756; worked, the end-member is 33.54% Cr2O3. Its index is 0.089 above pyrope’s and a 20.00 g piece would read 14.68 g in water, 0.26 g above pyrope. Grew et al. decode chrome pyrope as pyrope, and Cr-pyrope and chromium pyrope as pyrope or knorringite.
The trade names. The International Gem Society says chrome pyropes have very dark tone, that ants have brought them to the surface in Arizona, hence anthill garnets, and that they have also been found in Tanzania. Grew et al. decode anthill garnet as pyrope.
Colour change. The pyrope sheet records some examples as bluish green in daylight and wine-red in artificial light. The gem society describes Norwegian material, n = 1.747 and SG 3.715, as wine red in incandescent light and violet in daylight, and says colour-change stones from the Umba Valley, Tanzania are pyrope-spessartites. GIA’s garnet description says garnets can show a colour change similar to alexandrite’s; alexandrite itself is chrysoberyl, on is chrysoberyl the same as alexandrite.
Pyrope against spinel, almandine and ruby
The end-member gap: the sheet’s figures, 1.714 and 3.582, describe near-pure pyrope, and a gem sold as pyrope reads higher. The International Gem Society says pure pyropes are unknown in nature, that the purest gem-quality specimen contained about 83% pyrope, and that a non-gem Dora-Maira specimen reached 98%; the sheet’s Dora-Maira formula works out at 97.6% magnesium on the X site. The gem society gives gem pyrope 1.73 to 1.766 and SG 3.65 to 3.87, which read 14.52 to 14.83 g in water for 20.00 g. GIA’s garnet facts give the whole group 1.714 to 1.888.
Against spinel, a documented failure. Red spinel reads 14.41 to 14.44 g for 20.00 g in water and pyrope 14.42 g; their sheet indices, 1.719 and 1.714, are 0.005 apart, and the gem society’s ranges overlap from 1.730 to 1.735. Crystal form is the test on a crystal: pyrope dodecahedra or trapezohedra, spinel octahedra. The comparison is set out on spinel.
Against almandine and ruby. Almandine, 4.318 and n = 1.830 on its sheet, reads 15.37 g. Ruby is corundum and gives two refractometer readings; the rule is on corundum. Garnet, glass and doublets are on how to tell if garnet is real, and the rhodonite question on is rhodonite a garnet. The method for weighing is on how to measure specific gravity at home.
Where pyrope is found: Bohemia, Kimberley, Arizona
The Occurrence field: in ultramafic rocks, as peridotites, kimberlites, eclogites and serpentinites, and in hornblende-garnet-plagioclase rocks and anorthosites; also in amphibole and biotite schists; detrital. Its associates include ilmenite, phlogopite, olivine, pyroxenes, diamond, kyanite, rutile and omphacite. The International Gem Society says pyropes not only occur with diamonds but sometimes form as inclusions within them; the diamond question is on is diamond a mineral.
The Distribution field calls it widespread and names localities that have produced substantial amounts of gem material: around Mĕrunice (Meronitz), Czech Republic; immense crystals in the Dora-Maira massif, Piedmont, Italy; Zöblitz, Saxony, Germany; the diamond mines around Kimberley, South Africa; the Umba River and the Pare Mountains, Tanzania; Macon Co., North Carolina, and Buell Park, near Fort Defiance, Apache Co., Arizona; near Bingara, New South Wales, and Proston, Anakie and Ruby Vale, Queensland; San Martin and Quines, Argentina; and Gravata, Pernambuco, Brazil.
No British locality is on the pyrope sheet; the only Wales in its Distribution field is New South Wales, by script. Elie ruby is a name in Grew et al.’s list, not a locality on the sheet, and we add none. The rest of the reference section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.