Mutton fat jade is a trade descriptor for high-quality creamy white jade material, commonly nephrite.

Mystic Topaz profile is under factual gemological review. Properties shown here are provisional unless marked as verified.

Nephrite profile is under factual gemological review. Properties shown here are provisional unless marked as verified.

Nigrine is an ambiguous term in gem trade usage and should be tied to tested mineral identity before strict species claims.

Obsidian is a natural volcanic glass formed by rapid cooling of silica-rich lava.

Ocean agate is a trade-name patterned agate category rather than a separate mineral species.

Ocean jasper is a trade name for orbicular patterned chalcedony/jasper material, chiefly from Madagascar.

Ocean jasperite is a trade descriptor for patterned ornamental material, not a strict mineral species.

Ocean reef is treated as a broad trade label for decorative patterned material.

Olivine is a magnesium-iron silicate mineral; transparent gem-quality material is known as peridot.

Onyx is a parallel-banded chalcedony variety of quartz, traditionally black and white in layered form.

Opal is less about crystal form than about light. Depending on structure, it may show a soft inner haze, bold flashes of spectral colour, or a calm body tone that changes character as the stone is turned in the hand.

Orange Sapphire profile is under factual gemological review. Properties shown here are provisional unless marked as verified.

Among jewellery stones, Orange Spinel stands out for combining appearance with notable wear resistance. That combination of orange body colour, 9 Mohs hardness, and vitreous lustre is what usually makes it recognisable in practice.

Orthoclase is a monoclinic potassium feldspar species and an important member of the moonstone feldspar series.

Padparadscha Sapphire sits among the more resilient gem materials used for jewellery, which shapes both how it wears and how it is collected. That combination of blue body colour, 9 Mohs hardness, and vitreous lustre is what usually makes it recognisable in practice. The secondary sapphire blue note often matters more than people expect when separating it from lookalikes.

Paraiba spinel is a trade term for bright neon blue-green spinel resembling paraiba-style color appearance.

Paraiba Tourmaline profile is under factual gemological review. Properties shown here are provisional unless marked as verified.

Among jewellery stones, Peach Topaz stands out for combining appearance with notable wear resistance. That combination of blue body colour, 8 Mohs hardness, and vitreous lustre is what usually makes it recognisable in practice. The secondary orange note often matters more than people expect when separating it from lookalikes.

Pearl is an organic gem formed by mollusks, represented in trade by both natural and cultured products.

Peridot is easiest to understand by starting with green and brown colour. That combination of green body colour, 6.5 Mohs hardness, and vitreous lustre is what usually makes it recognisable in practice. The secondary brown note often matters more than people expect when separating it from lookalikes.

The appeal of Peruvian Blue Opal lies in what happens after the stone is turned in the light. That combination of blue body colour, opalescence, play of colour, iridescence optical effects, and 5.5 Mohs hardness is what usually makes it recognisable in practice. The effect is best judged in motion, since a static view rarely shows the full character of the stone.

Petrified wood is fossil wood in which original organic tissue has been replaced by silica minerals.

Phantom quartz contains internal growth-stage outlines recording episodic crystal development.