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Claus Hedegaard

Garnets

Specimen of Almandine from New South Wales, Australia Garnets are widely distributed in schists, granites, kimberlites, so-called skarns, and occasionally carbonatites, but comparatively few deposits produce attractive, collectible specimens. Garnets are simple silicates with two tri-valent and three bi-valent metal ions per unit. Garnets are highly miscible, that is a given specimen often contains important proportions of several species. The classic 'red' garnets, Pyrope, Almandine, and Spessartine, are sometimes lumped under the term Pyralspite (combining first two letters of the species' names) and the 'green' garnets, Uvarovite, Grossular, and Andradite, similarly under Ugrandite. This suggest either intermediate members, or more likely specimens of unknown composition. The Pyralspite and Ugrandite series are not appreciably miscible, except for the cinnamon coloured Grossular var. Hessonite, which is an iron-rich Grossular.
Garnet has been known since Antiquity under a number of different names. Most sources obviously refer to the red Pyralspite, as does ultimately the name garnet. After 1262 the author Albert Magnus applies the name 'granatus' to red garnets, referring to the colour of flower and fruit of pomegranate, and 'granat' is the term still used for garnets in German and Scandinavian languages. The term 'garnet' was introduced into English by Kirwan in 1794, and is now used for all members of the group, including the non-red ones. With other red minerals, red garnet has often been called Carbuncle, Karfunkel with antiquated terms - you will find this in the Bible and with Pliny. Theophrastus (app. 372 BC-app. 287 BC) in his work 'On Stones' included some garnets under the name anthrax.
Modern researchers have discovered a number of additional garnets, namely Calderite, Goldmanite, Hibschite, Hydrougrandite, Katoite, Kimzeyite, Knorringite, Majorite, Morimotoite, and Schorlomite. They have the same structure as the classic Pyralspite and Ugrandite, but different chemical composition. Furthermore, there are a number of varieties of garnet species with traces of alien elements - I mentioned the iron-rich Grossular var. Hessonite - but you may also come across:
Industrially garnet is used as an abrasive. It is generally not hard enough to cut stones, but being harder than Quartz it is excellent for softer materials as powder in air- abrasion of metals. Garnets have been used for gems since Antiquity, and are still popular today, whether as carefully faceted transparent stones, tumble-polished chips for necklaces, or occasional carved charms and small figurines.
My records indicate that garnets from a range of deposits occur on specimens that also carry one or more of the following minerals: Actinolite, Ägirine var. Ferro- schefferite, Ägirine var. Schefferite, Albite, Antigorite, Aragonite, Arsenopyrite, Aschamalmite, Astrophyllite, Bergslagite, Beryl var. Aquamarine, Biotite, Bismuthinite, Bityite, Bornite, Braunite, Calcite, Chalcopyrite, Chamosite var. Mg-Chamosite, Chromite, Chrysocolla, Chrysotile, Clinochlore, Columbite, Copper, Cymrite, Diopside, Dolomite, Ellenbergerite, Epidote, Fergusonite, Fluorapatite, Fluorapophyllite, Fluorite, Franklinite, Franzinite, Gadolinite, Galena, Gaudefroyite, Gilalite, Goethite, Hancockite, Hausmannite, Hedenbergite, Helvite, Hematite, Hendricksite, Ilvaite, Jennite, Johnbaumite, Junitoite, Kaolinite, Kinoite, Kyanite, Leuchtenbergite, Leucite, Leucophoenicite, Liottite, Långbanite, Magnesiochromite, Magnetite, Malachite, Manganaxinite, Margarite, Margarosanite, Marialite, Melanotekite, Microcline, Microlite, Millerite, Minehillite, Monazite, Mooreite, Muscovite, Oligoclase, Omphacite, Opal, Orthoclase, Pectolite, Pennine, Perovskite, Phlogopite, Pyrite, Pyrrhotite, Quartz, Rauenthalite, Rhodonite, Richterite, Ruizite, Sanidine, Sauconite, Scheelite, Shuiskite, Sphalerite, Spodumene var. Hiddenite, Staurolite, Svabite, Thortveitite, Thuringite, Titanite, Topaz, Tremolite, Vesuvianite, Willemite, Wollastonite, Xenotime, and Zincite.
Specimen of Almandine from New South Wales with four triple axes
Garnets are good to demonstrate the intricacy of the cubic crystal system - there are four triple axes, and

Specimen of Almandine from New South Wales with three quadruple axes
three quadruple axes. Note, it is the presence of four triple axes, that characterises the cubic system; the quadruple axes need not be there.

Specimen Handling

Garnets are stable in a normal household environment - it is one of the most stable and inert minerals known. They are not harmed by light, changes in temperature in the normal comfort range, or known to decompose. Garnets specimens can be fragile and should be handled with care like any other mineral specimen. Garnets are not appreciably soluble in water.

Bibliography

Albertus Magnus. 1262 or later. De Mineralibus
Anthony, John Williams, Richard A. Bideaux, Kenneth W. Bladh & Monte C. Nichols. 1995. Handbook of mineralogy, vols. 2.1 & 2.2
Bancroft, Peter. 1984. Gem & Crystal Treasures.
Bauer, Max. 1896. Edelsteinkunde, 1st ed.
Bauer, Max. 1909. Edelsteinkunde, 2nd ed.
Bauer, Max. 1968. Precious Stones, I-II. Dover Publications
Gaines, Richard W., H. Catherine W. Skinner, Eugene E. Foord, Brian Mason, Abraham Rosenzweig & Vandall T. King. 1997. Dana's new mineralogy: the system of mineralogy of James Dwight Dana and Edward Salisbury Dana, 8th ed.
Hintze, Carl (ed.) 1916-1929. Handbuch der Mineralogie, vol. 1, section 3, part 1.
Kirwan, R. 1794. Elements of Mineralogy, 2nd ed.
Mercier, A., B. Moine, J. Delorme & M.A.F. Rakotondrazafy. A note on a new occurrence of vanadian grossular garnet from Madagascar. Journal of Gemmology, 25(6),391-393
Noe-Nygaard, Arne. 1966. Mineralogi, 3rd ed.
Ramdohr, Paul & Hugo Strunz. 1980. Klockmann's Lehrbuch der Mineralogie, 16th ed.
Roberts, Willard Lincoln, Thomas J. Campbell & George Robert Rapp jr. 1990. Encyclopedia of Minerals 2nd ed.
Sinkankas, John. 1964. Mineralogy.

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