Click to donate today!
Kitto's Popular Cyclopedia of Biblial Literature
Agate, a precious or rather ornamental stone, which was one of those in the breast-plate of the high-priest (Exodus 28:19; Exodus 39:12). This stone is popularly known in this country under the name of Scotch pebble. There are few countries in which agates of some quality or other are not produced. The finest are those of India; they are plentiful, and sometimes fine, in Italy, Spain, and Germany; but those found in this country are seldom good.
Agate is one of the numerous modifications of form under which silica presents itself, almost in a state of purity, forming 98 per cent, of the entire mineral. The siliceous particles are not so arranged as to produce the transparency of rock crystal, but a semi-pellucid, sometimes almost opaque substance, with a resinous or waxy fracture; and various shades of color are produced by minute quantities of iron. The same stone sometimes contains parts of different degrees of translucency, and of various shades of color; and the endless combinations of these produce the beautiful and singular internal forms, for which, together with the high polish they are capable of receiving, agates obtain their value as precious stones. The Scripture text shows the early use of this stone for engraving; and several antique agates, engraved with exquisite beauty, are still preserved in the cabinets of the curious.
Kitto, John, ed. Entry for 'Agate'. "Kitto's Popular Cyclopedia of Biblial Literature". https://www.studylight.org/encyclopedias/eng/kbe/a/agate.html.