Characteristic features in ornamental materials Characteristic features in organic materials Observation by gemmological microscope Inclusions in cut and polished gemstones. Identification of gemstone species and variety. Distinguish natural gemstones from synthetics. Detecting treatments and composites Refractometer Measurement of refractive indices (RI) and birefringence (DR) to 3rd decimal place Identification of optic character and optic sign. Measurement of RI by distant vision method Polariscope and conoscope Crystalline character in isotropic, anisotropic and aggregate materials. Interference figures. Spectroscope Characteristic absorption spectra in gemstones related to the syllabus. Dichroscope Dichroism in coloured mono-crystalline materials Chelsea Colour Filter Colour effects fluorescence in some gemstones Ultra Violet Light Colour effects fluorescence in some gemstones Specific Gravity S.G. measurement and weigh estimation in gems Observation and testing of the following gemstones with all gemmological instruments as required Inorganic Gemstones and Synthetics Actinolite Ambligonite Andalusite Apatite Axinite Benitoite Beryl Calcite Cassitarite Chrysoberyl, Corundum Cubic Zirconia Danburite, Diamond, Diopside Enstatite Ekanite Feldspar group Fluorite Garnet group Glass- artificial Glass - natural Gypsum (including alabaster) Hematite Idocrase Iolite, Jadeite Kornerupine Kyanite Lapis Lazuli Malachite Nephrite Opal, Peridot Phenakite Pyrite Quartz group Rhodochrosite Rhodonite Scapolite Scheelite Serpentine (including bowenite) Sillimanite Sinhalite Sodalite Sphene Spinel Spodumene Steatite (soapstone) Strontium Titanate Synthetic Moissanite Synthetic Rutile Taaffeite Tanzanite (Zoisite)
Accessories Sub-stage accessories: Polarizing filters, one in the body tube and the other below the stage to produce crossed polarized light. Iris diaphragm to control transmitted lighting through the adjustable circular aperture. Immersion cell. To observe a gemstone immersed in a fluid with refractive index close to that of the stone. This makes the effect of the surface features almost invisible such as reflection of light from facets. Internal details become more clearer, such as colour concentration and growth lines. Colour concentration on facet edges in surface diffusion treated sapphires are observed under this condition. Uses of the microscope: a. All types of observations of as with 10 X lens, but in details when necessary. b. Observations of inclusions, the interior features of gemstones. i. Under ordinary light. Transmitted light may be used either as dark field or bright field illumination, with or without overhead illumination; • All types of interior features in gemstones, which are collectively called inclusions. ii. Under plane polarized light, which is made to transmit through the gemstone. • Some internal features such as growth planes, twinning planes, pleochroic colours in mineral inclusions etc. • Pleochroism in coloured anisotropic gems. Pleochroic colours seen separately. iii Under crossed polarized light. (Used as the polariscope) • Observations as seen under the polariscope • Tabby extinction in some gems as in synthetic spinel, hessonite garnet etc. • Detect anisotropic mineral inclusions in isotropic gemstones. • Twinning planes, halo effect as in zircon inclusions etc. iv Under crossed polarizing filters with convergent light: • The interference figures for uniaxial and biaxial gems c. The use of the spectroscope in conjunction with the microscope to observe the absorption spectra in gemstones. d. Determination of approximate refractive indices by; •• Direct measurement method through real depth and apparent depth of the gemstone