The word “opal” is derived from the Latin OPALUS, and is identified with the Sanscrit UPALA, a precious stone. It appears under the forms opale, opall, opalle, opalis, ophal. This beautiful inimitable gem is a hydrous silica, and is allied to the non-metallic minerals of the agate family from which, however, it differs in brilliancy, lustre and degree of hardness. It is sensitive to the action of strong chemicals and does not present, like other minerals, crystalline form. As a gem of the Sun it exhibits flows of fire like the sun at midsummer—as a gem of Venus its delicate beauty radiates her colourful charms, and as a gem of Uranus its refusal to submit to the all-embracing law of mineral structure harmonizes with the iconoclastic character of that planet according to astro-philosophy. Ancient and modern poets unite in singing the praises of the opal. Onomacritus, known as the religious poet of the ancient Greeks, over 2,400 years ago wrote that “the delicate colour and tenderness of the opal reminded him of a loving and beautiful child.” Joshua Sylvester (16th century) writes of “the opal-coloured morn,” and the poet Campbell of a time when “the opal morn just flushed the sky,” thus echoing William Drummond of Hawthornden’s: “_Aurora ... with her opal light Night’s horrours checketh, putting stars to flight._” Emerson writes of the “opal-coloured days,” and Poe with true poetic fancy sees even the air opal tinted: “_A wreath that twined each starry form around And all the opal’d air in colour bound._”