Keywords
Abstract
Opal, a word originated in the sacred language of the Hindus, from the term upala, means precious stone. This gem has enchanted people throughout history for its variety of colorful flashes, unmatched in the mineral kingdom. This article aims to present the opals found in Pedro II and Buriti dos Montes, Piauí, Brazil, which produce quality opals since the 1940s. Due to their hydrothermal genesis, they have unique gemological characteristics. In Pedro II are found light opal (the most frequent), boulder opal, matrix boulder, black opal (rare) and composite opals (doubles and triplets) exhibiting the color play patterns pinfire (little cowl), block, flagstone, jigsaw, flash fire, broad flash (stove), tiger, ribbon, harlequin, harlequin flag and rolling flash. In Buriti dos Montes, the orange opal (fire opal or jelly) occurs, exhibiting the hues of light yellow water, light yellow, yellow, yellow-orange, orange, reddish-orange, red, dark red and red. brownish; pale blue and white opals were also found. More research is needed to discover the potential and gemological characteristics of opals found in several municipalities in Piauí.