Section
Physical Sciences
Abstract
Apple green gem quality chrysoprase from haneti-Itiso area, central Tanzania was studied. Under the microscope the chrysoprase shows highly disordered spherules which are concentric. Composed of bipyramidal quartz, chalcedony quartzite and opal-A. The spherules were classified into four main types according to the shell arrangement. The diameter of the spherules ranged from 40 μm 77 μm. Fluid inclusion types in bipyramidal quartz were monophasic low temperature type. Mineralogical properties indicated refractive indices to be 1.548 to 1.553 (±0.002), mean specific gravity 2.56, hardness about 7 on Moho’s scale, inert to ultraviolet radiation, green though Chelsea filter, and absorption in the deep red and violet part of the optical absorption spectrum. X- ray diffraction determinations showed that the chrysoprase consists mainly of alpha-quartz with some opal-CT. atomic absorption spectrophotometry (AAS) deteminations revealed a high Ni content, 0.55 wt% and low Co and Cr contents of 120.0 and 1.0 ppm respectively. Neutron activation analysis (NAA) determinations revealed near chondritic Rare earth elements (REE) contents. The determinations confirms the identity of the material to be chryoprase and the spherules, silica types, and rare earth element contents suggest that the chrysoprase was deposited by evaporation of surface waters connected with silicification of serpentinities.
Recommended Citation
MALISA, E.P.
(1995)
"Silica spherules in chrysoprase from haneti-itiso area, cental tanzania,"
Tanzania Journal of Science: Vol. 21:
Iss.
1, Article 3.
Available at:https://doi.org/10.65085/2507-7961.2421
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
