Gemstone & Crystal Guides

What a certificate usually shows

• Photo of the stone
• Weight in carats, which should match the listing
• Measurements in millimetres and shape/cut
• Colour description
• Test results such as refractive index (RI) and specific gravity (SG), which help identify the mineral
• Identification, for example “Natural Blue Sapphire” or “Natural Corundum”
• Comments, which may mention treatments such as heating, oiling or filling

Natural, synthetic and imitation

• Natural: formed in the earth
• Synthetic (lab-grown): same mineral, made in a lab
• Imitation: a different material, such as glass, made to look similar

For astrology, natural stones are traditionally preferred. At G for Gemstones, Thailand-origin stones are labelled by origin rather than described as natural.

Simple checks before you buy

• Match the carat weight and photo on the certificate to the listing
• Be wary of prices far below the market for the same weight and origin
• Natural stones usually show small inclusions; perfectly clean, cheap stones deserve questions
• Ask for a video of the exact stone

Does every stone need a certificate?

For primary Navratna stones, yes. For low-cost crystals and bracelets, a purity or authenticity card is common.

Frequently asked questions