b'GarnetFeatureFigure 4 shows a finished faceted pyrope, pyrope-almandine (rhodolite) rough, and gemmy striated spessartine rough.Garnet in earlier timesPrecious and semi-precious stones were long prized in antiquity for their beauty and supposed medicinal and magical properties. In the Old Testament of The Bible (6th BC) garnets were listed as part of the adornment of princes (Ezechiel: 28, 13).A seminal treatise On Stones was produced in the 4th century BC by Theophrastus, a pupil of Aristotle. This work recognised the red garnet by the generic term, anthrax, a glowing live coal, because a garnet held up to the sun seemed similar. Anthrax also could have meant red spinel and ruby. Theophrastus noted anthraxs use a seal-stone. Many red garnet seal-stones from this era now reside in museums, but none of red spinel or ruby (both harder than garnet), so anthrax was red garnet in Hellenistic time (Caley & Richards, 1956). Garnet, with its less than extreme hardness (H7 ), was readily carved intaglio (sunken design) and cameo (raised design) by the technology of the periodvarious drills and wheels coated withFigure 2.Five dodecahedral garnets with rhomboid faces: (back left) powdered emery (impure corundum) or pulverised diamond. almandine from the Thackaringa area to the southwest of Broken Hill NSW, weight 963 g; (back right) almandine from Harts Range NT, 201 g; (front left) Garnets were sourced mainly from Asia after the 4th Centuryalmandine from India, 57 g; (front middle) almandine Harts Range, 11 g; (front conquests of Alexander. They were a popular stone in rings andright) grossular from Mexico, 25 g. Specimens such as these, although not for ornamental use (Hornblower and Spawforth, 2012). gemmy, are popular with collectors. The largest garnet shown is worth ~ $150, the grossular ~ $10 (scale in cm).Pliny the Elder (AD 23-79) discussed garnets at length in Book 37 of his Natural History (Eichholz, 1971). Pliny called garnet the carbunculus because good quality reddish gem garnet, probablyFurthermore, in each variety (of garnets) the more brilliant of the pyrope-almandine variety, looked warm, suggestive ofstones are called male and those of weaker lustre femaleburning carbo, charcoal/coal. There is a reason for this. Lustre is an important quality for any gem Garnets vary in lustre. Pliny (37, 92-3) commented on this twoand especially so for garnet: brightish vitreous lustre stones are millennia ago: common; brilliant sub-adamantine lustre stones are not and are far more valuable. The percentage of light reflected from a smooth (carbunculi) praeterea in omni genere masculi appellantursilicate or oxide surface depends on the materials refractive acriores et feminae languidius refulgentes index (velocity of light in vacuum / velocity of light in material, R.I. always 1). Through the Bohr Equation (see Bloss, 1971): the higher the R.I. the higher the reflectivity. The R.I.s for grossular, almandinepyrope, and andraditedemantoid are 1.73, 1.77, and 1.89 respectively (diamond is 2.42). The high R.I.s for andradite-demantoid impart a lively reflectivity attractive to the eye.Figure 1.Ranges in garnet densities, based on Gemmological Institute of America (GIA) data 1995 and Schumann (2006). Rhodolite is a 2:1 pyropealmandine solid solution mix. Grossular with Fe is hessonite and with V, Cr isFigure 3.Translucent gem garnets variously cut and polished. These tsavorite. Andradite with Cr, Fe is demantoid, with Fe is topazolite, and with Fe,are of the common vitreous lustred almandinepyrope low value type, Ti is melanite. Colours depicted are approximate and do vary in each type. Theand it is thought that they derive from India. The single stone in the centre natural density variations are due to solid solution mixing in the garnet mineralforeground weighs 0.28g (1.4 carat) and has lateral dimensions 9 x 6 mm, it series (e.g., pyrope and almandine), and to mineral inclusions. See Table 1 foris worth ~ $10. Most gem garnets are small, weighing between 0.2 and 2.0g formulae of the main garnets. (1 to 10 carats).65 PREVIEW DECEMBER 2021'