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Diamond is the only gemstone composed of a single element — pure carbon in a cubic crystal lattice. It is the hardest natural mineral (10 on the Mohs scale) and has the highest thermal conductivity and exceptional light dispersion among all gemstones. It forms at pressures of 45–60 kilobars and temperatures of 900–1300°C deep in the Earth's mantle, brought to the surface by volcanic eruptions through kimberlite pipes.

Ruby is the red variety of corundum (Al₂O₃), colored by chromium oxide. It is one of the four classical precious gemstones alongside diamond, sapphire, and emerald. With hardness 9, it ranks just below diamond — exceptionally durable for everyday wear. The finest rubies, known for "pigeon's blood" color, come from the Mogok Valley in Burma.

Sapphire is any corundum that is not red enough to be a ruby — "sapphire" without a qualifier always means blue. The blue color arises from a combination of titanium and iron. Kashmir sapphires from the 1880s are the absolute quality reference: an unreproducible velvety blue with milky light scattering that cannot be replicated.

Emerald is the green variety of beryl (Be₃Al₂Si₆O₁₈), colored by chromium and/or vanadium. It is one of the four classical precious gemstones and the only one where inclusions are not just expected but even accepted. Due to complex crystallization in metamorphic rocks, emeralds never grow flawlessly — a "clean emerald" is actually rarer than a "clean ruby or sapphire."

Tanzanite is the blue-violet variety of zoisite, discovered in 1967 at the foot of Kilimanjaro in Tanzania. It is one of the rare precious gemstones found in a single location on Earth — the Mererani mine covers only 20 km². Tiffany & Co. named the stone and launched it to market. GIA included it in the "Big 3 colored stones" alongside ruby and sapphire.

Spinel is the mineral magnesium aluminate (MgAl₂O₄), occurring in a rich color spectrum. For centuries it was unrecognized and confused with ruby — the most famous example is the "Black Prince's Ruby" in the British Crown, which is actually a 170-carat spinel. Today, spinel is valued in its own right, especially the red "Jedi spinel" from Burma and the vivid pink Mahenge spinel from Tanzania.

Amethyst is the purple variety of quartz (SiO₂), colored by ionized iron in combination with natural irradiation. Throughout history it was valued equally to rubies and sapphires — until massive deposits were discovered in Brazil in the 19th century, "demoting" it to a semi-precious stone. Today, amethyst is the most popular purple gemstone in the world.

Aquamarine is the light blue to blue-green variety of beryl — the same mineral as emerald. The name derives from Latin aqua marina (sea water). Aquamarine is one of the rare colored gemstones that is often naturally very clean — inclusions are the exception, not the rule. Pakistani specimens from the Shigar Valley are prized for exceptional blue color and transparency.

Alexandrite is chrysoberyl (BeAl₂O₄) with an exceptional optical color-change phenomenon: vivid green in daylight, reddish-violet under incandescent light. This phenomenon — called the "alexandrite effect" — results from selective light absorption by chromium, which absorbs wavelengths where human vision and light spectrum are balanced between red and green. Discovered in 1830 in the Urals, named after Tsar Alexander II.

Tourmaline is a group of borosilicate minerals with a rich color spectrum — occurring in virtually every color, often multicolored within the same crystal. Color is given by different elements: manganese (pink, red), iron (blue, green, yellow), chromium (intense green), copper (electric blue Paraíba tourmaline). It is one of the minerals with the highest piezoelectric and pyroelectric effect — the crystal becomes electrically charged under pressure or temperature change.

Citrine is the yellow to orange variety of quartz, colored by iron impurities. The name derives from Latin citrus (lemon). Natural citrines with intense color are relatively rare — most commercial citrine is heat-treated amethyst or smoky quartz. Madeira citrine with deep red-orange color is the most prized variety.

Garnet is not one mineral but a group of chemically related minerals with the same crystal structure. The general formula X₃Y₂(SiO₄)₃ allows for enormous variation. The most common is red almandine garnet, but green (demantoid, tsavorite), orange (spessartine, hessonite), purple, and even rare blue and color-change specimens exist.

Opal is a unique mineraloid — an amorphous form of hydrated silicon dioxide (SiO₂·nH₂O). Its unique property is "play of color" — an optical phenomenon where the stone displays a rainbow of moving colors. It forms by the sedimentation of colloidal silica spheres into rock cavities, which then diffract light.

Pearl is a unique organic gemstone — formed in mollusks (oysters and clams) as a defensive mechanism when a foreign object enters. The mollusk secretes nacre (mother-of-pearl) around the intruder in concentric layers. It is the only gemstone created by a living organism. Natural pearls without human intervention are extremely rare today — what's on the market are cultured pearls.

Morganite is the pink to peach variety of beryl (same mineral as emerald and aquamarine), colored by manganese ions. Named after banker and gem enthusiast J.P. Morgan in 1910. In the past decade it has become one of the most popular gemstones, thanks to the rose gold jewelry trend with which its warm color perfectly harmonizes.

Peridot is the gem variety of olivine (Mg,Fe)₂SiO₄, one of the rare stones that comes in a single color — olive green to vivid green (color given by iron, not impurities). It is one of the rare gemstones formed in the Earth's mantle (not crust) and has been found in meteorites (pallasites). Cleopatra's "emeralds" may have actually been peridots from Zabargad Island.

Moonstone is a variety of orthoclase feldspar with the exceptional optical phenomenon of adularescence — a bluish to white light "glow" that moves across the stone like a reflection of moonlight. It is one of India's precious gemstones and the stone of Hindu goddess Lakshmi. Ceylon moonstones with blue sheen on white body are the absolute quality reference.

Topaz is aluminum silicate fluoride (Al₂SiO₄(F,OH)₂) with hardness 8 — an exceptionally hard and durable gemstone for wear. It comes in a rich palette of colors: naturally colorless, yellow, orange, pink, blue, and green. "Imperial topaz" — exclusively from Brazil, in vivid orange to peachy color with reddish overtones — is the absolutely most valuable variety.

Zircon is one of the oldest minerals on Earth — the oldest known zircon crystal (Jack Hills, Western Australia) is 4.4 billion years old. It is a natural mineral that must be strictly distinguished from synthetic cubic zirconia (CZ) — these are completely different substances. Natural zircon has among the highest refractive index of all natural gems and one of the best dispersions.

Kunzite is the pink to violet-pink variety of spodumene (lithium pyroxene), colored by manganese. Named after gemologist G.F. Kunz in 1902. Comes in exceptionally large crystals — stones above 100 ct are not unusual. Has intense pleochroism: different colors viewed from different crystal axes (pink, violet, colorless). Known for exceptional clear pink color reminiscent of morganite but more violet.