New physical, geochemical and gemological data of opals from Acari Mine (Arequipa Department, Peru)
Caucia, Franca; Marinoni, Luigi; Leone, Alberto; Ghisoli, Christian
published: Jan 1, 2015
ArtNo. ESP154019201004, Price: 29.00 €
The physical and compositional properties of some opals from Acari Mine, Peru, have been investigated through several methodologies like optical analysis, specific gravity, refractive indices, XRPD, LA-ICP-MS, SEM, AvaSpec-2048 optical spectrometry. The opals show different colors: green, green-blue, pink, dark pink, with a greasy luster. Play of color has not been observed. Specific gravity and reflective indices are consistent with data available in literature. XRPD analyses highlighted Acari Mine opals are CT types with variable contents of cristobalite and tridymite. The most abundant impurities are Mg, Al, Na, Ca; Cu and Mn appear to be cromophore elements that determine the green and the pink colors respectively. A distinct feature of the dark pink opals from Acari Mine is represented by the presence of β-carotenoid and quinoni visible in the absorption spectra obtained with AvaSpec-2048 spectrometer. Mg and Al are related to the abundant presence of sepiolite (green opals) and palygorskite (pink opals). SEM investigations highlighted different textures that are typical of magmatic CT opals.