Doğu Anadolu’daki Geç Miyosen volkanizmasının örneklerinden biri olan Yamadağ Volkanitleri Malatya ili

Yamadağ Volcanics which is one of the examples of the Late Miocene volcanism in Eastern Anatolia covers largeareas within the boundaries of Arguvan county of Malatya. The gemstones, subject of this research range from afew centimeters to about 30-40 cm in size and are formed in the cavities of the basalts beonging to Yamadağvolcanics. These gemstones seem to have formed as veins extending in east-west direction and consist of opal (opal-CT) and chrysocolla. Opal formations have various colours such as white, brown, yellow and greenish, while chrysocolla formations are bluish-greenish in color. both opal and chrysocolla are of massive type and their freshsurfaces display waxy luster. Mineral paragenesis and formation conditions of gemstones and are determined byapplying XRD, SEM, FT-IR techniques. ICP-MS technique is used for the determination of the geochemicalcompositions. The gemological characteristics are identified via cabochon and facet cut techniques by usingdiamond coating blade, sintered diamond abrasive discs and polishing machine. Opals are usually composed oftridymite minerals, also in some cases quartz and cristobalite minerals accompany the tridymite minerals. The EDXmeasurements reveal, enrichment of Fe and Al in opals, and of Cu in chrysocolla. The ICP-MS measurements, in chrysocollas reveal, enrichments in LIL elements such as Ba, Sr and in HFS elements such as U. Consequently,gemological studies show that the chrysocolla and opals in study area, which have waxy luster and massivestructure, are suitable for utilization as a gemstone due to its color, hardness, durability, homogeneous distributionof color and processability