Garnet, the name of a mineral species, presenting many varieties; also applied by Dana to designate a section of the silicates; and in geology it is the name of a rock made up of some variety of the mineral. The garnet is supposed to have been sometimes included by the ancients in their names carbunculus and hyacinthus. In its more perfect forms it is a gem, and when cut and polished bears some resemblance to the ruby in color, transparency, and lustre. Some of the precious varieties are distinguished by the names Syrian and oriental, and also almandine, from Alabanda, the place where in the time of Pliny they were cut and polished. These and the black varieties also have been much used in Europe, strung together like beads for necklaees. Those most esteemed in jewelry are obtained from Ceylon, Pegu, and Greenland. A single crystal of only 8 1/2 lines by 6 1/2 has been sold for about $700. Its crystals are rhomboidal and trapezoidal dodecahedrons and variously modified forms. Its hardness is from 6.5 to 7.5; specific gravity 3.15 to 4.3. It is met with of various colors, as red, brown, black, yellow, white, and green, and with a vitreous or resinous lustre.

According to its composition it has been divided into six sub-species, all of which pass into one another by insensible shades of difference; they are all silicates of different protoxides or peroxides; as: 1, the alumina-lime garnet, a silicate of alumina and lime, of which the cinnamon stone or essonite is an example; 2, the alumina-magnesia garnet; 3, the alumina-iron garnet, a silicate of the protoxide of iron and lime, as almandine and a variety of the common garnet; 4, alumina-manganese garnet, called also manganesian garnet; 5, iron-lime garnet, composed of silicates of the peroxide of iron and of lime, as the black garnet and a variety of the common garnet; 6, lime-chrome garnet, as the emerald-green ouvarouvite of Russia. The silicic acid in these varies from 34 to 44 per cent. Their composition is represented by the general formula 3RO, R2O3, 3SiO2, in which RO represents either one of the protoxides that may be present, and R2O3 either the alumina (A12O3), or the peroxide of iron (Fe2O3), or of chrome (Cr2O3). According to Odling, the formula is R2V2Si04, in which R=Ca, Mg, Fe, or Mn, and V=Fe, Al, or Mn. Garnets are easily melted by the blowpipe; and some varieties, as the melanite or black garnet found in the lavas of Vesuvius, appear to be a direct product of the fusion of their ingredients.

The iron-lime garnets, of which this is a variety, containing from 20 to 30 per cent. of peroxide of iron, and about the same proportion of lime, might be advantageously employed both as iron ore and flux in the manufacture of iron, mixed with other ores more rich in iron and deficient in silica. They frequently occur in the vicinity of iron ores, and in beds of great extent, forming a true garnet rock, and from their highly ferruginous appearance have in some instances been mistaken for iron ores.-Crystals of garnet are common in the granite rocks and the metamorphic slates and limestones in almost all localities where these are found; but when most abundant and large, they are commonly rough and unsightly. In the gold region they abound in the slates, and in some instances where the rock that contained them has crumbled away they are left loose upon the surface, so that they might easily be shovelled up by cart loads.