Mina La Sorpresa was mined for amethyst in 1997-1998 by employees of Mike New, Wayne Thompson and Ruben Avila. Some of the more prolific sites retain their claim names (Margarita, Valenciana, Palo Verde, Santa Rita, mina Amatitlan, Altamirano, Rayas, Sorpresa) whereas the names of many other diggings are now lost. These are mined by trenching and tunneling to a depth of 8 or 10 meters the workings are then abandoned in favor of searching out new veins. The 2.5 tons Empress of Uruguay is slightly less impressive after a tourist pinched a piece of the worlds largest amethyst on show in Queensland, Australia. The locality, first worked extensively in 1930-1933, is often cited as the small town of Amatitlan (or sometimes the neighboring town of Iguala, or as the Rio Balsas district), but in fact the amethyst has come from many veins scattered throughout the mountains northeast of Amatitlan. Sinkankas (1997) reported that fine faceted gems to 200 carats have been cut, and that one pocket of crystals may have yielded as much as $500,000 in gem rough! The rich color of Guerrero amethysts brings good prices on the gem rough market. The crystals are often found coated by manganese oxide. Clusters tend to be somewhat divergent and highly attractive.

Color patterns vary greatly between occurrences and even within individual pockets many finds are sufficiently characteristic in habit or coloration to be immediately distinguished from specimens from other pockets.Ĭrystal sizes in the 5 to 10-cm range are not uncommon, and rare individuals over 60 cm and 45 kg have been found (Wayne Thompson, personal communication). Rarer crystals are concentrically zoned, with nondescript milky outer zones concealing rich purple interiors. The amethystine color-a deep reddish purple comparable to the best Siberian amethyst-is generally very dark and rich in the core of the central and lower area but fades to colorless/white at the outermost zones and the termination (most Las Vigas crystals become darker toward the termination, and are nowhere as dark as the Guerrero crystals). At Guerrero the elongated amethyst crystals tend to be a bit fat around the lower and middle area, and taper to typical quartz terminations (Las Vigas crystals are rarely tapered).

Guerrero amethyst is easily recognized, and distinguished from Veracruz amethyst, by the crystal shape and coloration. The Guerrero amethyst mines are famous among mineral collectors worldwide as one of Mexico's two great sources of fine amethyst specimens-the other being the Las Vigas mines in Veracruz (see the article by Lieber and Frenzel in the Mexico-III special issue. Few outsiders have ever visited this dangerous area, known as much for opium production as for amethysts, but fine specimens and high-quality gem rough continue to emerge periodically from many small but similar deposits worked by the local people. Some of the finest amethyst specimens in the world have come from the remote mountains of the Sierra Madre del Sur of north-central Guerrero State in Mexico.

Newly discovered amethyst caves