Klassifikatsiya blagorodnykh matrichnykh opalov

Among all types of gemstones, a special place is occupied by the so-called precious matrix opals, rocks in which pores and interstices are filled with precious opal. In spite of the external similarity, these are rocks of different origins from quartzites and sandstones (Australia) to volcanic tuffs (Honduras).Differences in the mineralogical and petrographic composition, gemmological properties, and other features allow them to be classified according to thesecharacteristics. The proposed classification includes several groups of the most common matrix opals on the market: Solid Matrix Opal (Andamookamatrix), Concrete Matrix Opal, and Sandstone Matrix Opal. The study of the porosity of all groups of Australian matrix opals showed a significant diffeence of these formations according to this parameter. Thus, the open porosity of solid matrix opals was 0.52%, concrete 6.7%, and sandstone opal 18.6%. Matrix opals from Honduras were also examined as visually similar to the Australian matrix opals, but having a different genesis. Classificationof precious matrix opals has both scientific interest and a practical one in the diagnostic and assessment in gemmology.

Gemology, matrix precious opal, opalized rocks, concrete, carbonation, improvement proces