Jade is popular among Chinese. In gemmology, however, only two minerals are recognised as jade:nephrite and jadeite. Many jades sold on the market are treated to enhance their beauty. The tests described here are by no means exclusive but are some of the common means for differentiating various kinds of jade. Nephrite Jadeite Mineral Classification A member of isomorphous series of tremolite and actinolite of the amphibole group Pyroxene group Chemical Composition Hydrous Magnesium-iron Calcium Silicate Ca2(Mg, Fe)5Si8O22(OH)2 Sodium Aluminium Silicate NaAl(SiO3)2 Crystal System Monoclinic Monoclinic Crystal Habit Polycrystalline to cryptocrystalline. Interlocking masses of microscopic fibrous crystals Polycrystalline to cryptocrystalline.?Granular to fibrous interlocking structure Hardness 6.5 Approx. 7 Specific Gravity 2.8 - 3.1 3.30 - 3.36 Cleavage Perfect in 2 directions: 124o and 56o Imperfect in 2 directions at 87o and 93o Fracture Uneven to splintery Sugary, hacky Colour White to yellowish and reddish, dark green, black, also grey, brown White, green, mauve, blue, orange, brown to black Lustre Greasy to vitreous Greasy to vitreous Refractive Index 1.62 1.65 - 1.67 Locality China, New Zealand, Canada, Russia, USA Upper Myanmar, Japan, California, Russia Remark Most precious jade material in ancient China Not known to China before early Ching Dynasty Jade Simulants Translucent emerald, prehnite, chrysoprase (chalcedony), bowenite (serpentine), californite (idocrase), hydrogrossular garnet, aventurine quartz (Australian jade), dyed quartzite, dyed marble, glass and plastics Terminology in modern jade trade: A Jade: Natural jadeite without treatment; this class has nothing to do with quality i.e. colour and transparency. B Jade: Dark impurities (such as iron oxides) corroded by strong acids and the material consolidated with resin. C Jade: Dyed jadeite. B + C Jade: Jadeite subjected to the above two treatments. Identification: 1.Tests for jade simulants 1.1 Jadeite is an aggregate. The first step of identification is by observation or using polariscope (a pair of crossed polarizing filters) to check the stone whether it is a single crystal or an aggregate. 1.2 To test SG and, or, RI to determine the mineral type. 1.3 Plastic is warm in touch.? Glass has bubbles or micro dendritic structure (devitrification). Chrysoprase is apple green in colour. Aventurine quartz is dotted with green spots of fuchsite (green mica). Serpentine has a waxy lustre. Dyed quartzite and marble are like C Jade where green colour is concentrated at grain edges and cracks; the latter is effervescent in dilute HCl. 2. Tests for jadeite vs. nephrite 2.1 Observation: In general, nephrite is an aggregate of microscopic fibrous crystals; hence a weaker lustre than that of jadeite. 2.2 Hardness: The Chinese name of jadeite is hard jade and nephrite is soft jade. In other words, jadeite can scratch nephrite; however, this destructive test is not applicable to jade jewel in gemmology. 2.3 Hydrostatic weighing method: If the j ewel is not set in ring or other matter/material, to test the SG is a convenient method. 2.4 Use refractometer to obtain the RI figures for comparison (see table above) 3. Tests for B Jade 3.1 Observation: (1) B jade has a weaker lustre (waxy) than most types of natural jadeite but the green colour is sometimes too bright with that lustre. (2) Under magnification, the crystal edges are fuzzy because of the solution and destruction of individual grains after acid bath 3.2 Infra-red spectrum: Infra-red spectroscopy can detect the existence of resin in the tested sample 3.3 Fluorescence: The resin may exhibit bluish white fluorescence under long wave ultra-violet light 4. Tests for C Jade 4.1 Observation: Under 10X lens, green colour is seen being concentrated at grain edges because the dye stuff occupies the space among individual crystal grains. 4.2 CCF: If the dye stuff is (most often) chromic oxide to give green colour, the C Jade appears red when being viewed under a Chalser Colour filter 4.3 Absorption spectrum: The natural jadeite may have an absorption line at red region (existence of chromium, 640-650 nm) and blue-violet (existence of iron, 450 nm). The C Jade has a wider band at red. This issue of Geobits is contributed by Mr. William C.H Chow