mineralogy-gemmology
What is Nine-Dragon Jade? — A Gemmological and ...
Jade of the Nine Dragons (Hua'an Yu): gemological, historical investigation of a Chinese cultural jade.
What is Nine-Dragon Jade? — A Gemmological and ...
Jade of the Nine Dragons (Hua'an Yu): gemological, historical investigation of a Chinese cultural jade.
Obsidian, formation, history, deposits, use, co...
Chemical formula : 70–75% SiO2, plus MgO, Fe3O4 (composed mainly of silicon dioxide) Crystal system: amorphous Density: 2.25 to 2.40 Hardness (Mohs scale): 5 to 5.5 Refractive index: 1.480 to 1.500...
Obsidian, formation, history, deposits, use, co...
Chemical formula : 70–75% SiO2, plus MgO, Fe3O4 (composed mainly of silicon dioxide) Crystal system: amorphous Density: 2.25 to 2.40 Hardness (Mohs scale): 5 to 5.5 Refractive index: 1.480 to 1.500...