All you need to know about gemstones 

Precious vs semi-precious

Nowadays we don't tend to refer to gemstones in this way as much as we have seen throughout history, and "precious" tends to be used as marketing shorthand or to describe very rare types of gemstone. 

The term "precious gemstone" stems from medieval Europe and during the Renaissance, when only four gems - diamond, ruby, sapphire and emerald - were considered worthy of royalty. They were prized for their beauty, extreme hardness, rarity in known mines, and the lore surrounding them (e.g. emeralds’ supposed powers of foresight).

Precious Gemstone	Key Characteristics
Diamond	Exceptional hardness (10 / 10 on Mohs), unmatched brilliance
Ruby	Rich red “pigeon’s blood” color, hardness 9
Sapphire	Typically deep blue (but all colors), hardness 9
Emerald	Vivid green, often included (internal fissures), hardness 7.5

 

This legacy naming convention has continued into today, with only those 4 varieties technically categorised as "precious". All other gemstones are considered to be "semi-precious" - of which there are hundreds! The most commonly seen in jewellery tend to be: 

Gemstone	Family/Species	Mohs Hardness		Notes on Rarity
Amethyst	Quartz	7		Very common; high clarity stones more prized
Aquamarine	Beryl	7.5–8		Large, deeply blue crystals scarce
Tourmaline	Multiple species	7–7.5		Paraíba (electric blue) extremely rare
Tsavorite	Garnet family	7–7.5		Discovered 1960s; few deposits exist
Tanzanite	Zoisite	6–7		Only mined in Tanzania, 1967–present
Opal	Hydrated silica	5.5–6.5		Black opal from Lightning Ridge is among the rarest
Spinel	Spinel family	8		Often mistaken for ruby; Kashmir red spinels are ultra-rare
Topaz	Silicate	8		Imperial topaz (orange-pink) scarce; most topaz is pale

 

Rarity of gemstones

There are a variety of factors that can influence the rarity, and therefore market value, of gemstones. 

Geological Occurrence

• Common: Quartz varieties (amethyst, citrine) are widespread.
• Rare: Red beryl (bixbite) and Colombian trapiche emeralds form in only a handful of locales.

Colour Saturation & Clarity

• Pure, intense hues command premiums (e.g. “pigeon’s blood” rubies).
• Stones with fewer inclusions (internal flaws) are more sought-after - even emeralds, which normally contain inclusions, fetch top prices when exceptionally clear.

Size (Carat Weight)

• Larger crystals are exponentially rarer. A 5ct sapphire of top colour can be worth far more per carat than a 1ct of the same quality.

Cut & Treatment

• Expert cutting maximises brilliance and colour.
• Untreated stones (no heat, irradiation, or oiling) are rarer and carry a price premium.

Market & Fashion Trends

• Rarity in the earth doesn’t always equal rarity in demand. For instance, tanzanite is geographically limited (found only in Tanzania), but since its discovery in the 1960s, popularity has driven prices sharply.