The value of a gem depends on its colour, rarity and durability. Ruby, sapphire and emerald are gems that are commonly found. When choosing a gem, its colour, transparency, clarity and cut shall be taken into account.
Sources and Types of Semi-precious Stones
Semi-precious stones refer to the gemstones other than diamond, sapphire, ruby and emerald. Semi-precious stones are natural gemstones. The production of semi-precious stones is higher than that of gemstones. While there is no universally accepted grading system for semi-precious stones, the quality of a semi-precious stone may be generally determined by its colour and clarity. Common semi-precious stones include tourmaline, olivine, garnet, opal, spinel, zircon, turquoise, obsidian, amber and coral.
Tourmaline becomes electrically charged when heated. Tourmaline, which is quite brittle, crystallises in the hexagonal system. It occurs as prismatic crystals with triangular cross-section and obvious striations. Tourmaline was widely used in ornaments in the palace in the Qing Dynasty, and was said to be Empress Dowager Cixi’s favourite. It is also very popular nowadays. Tourmaline comes in a wide variety of colours, ranging from black, green, red, pink, yellow to blue. Light blue tourmaline is the most valuable variety. Watermelon tourmaline takes its name from its colour which is red in the centre and green around the outside, looking like a cut watermelon.
Obsidian is naturally occurring volcanic glass formed as a result of rapid cooling of lava. It is usually black, and may be brown, grey, red, blue and green. It may be single-coloured, striped or spotted.