Gemstone families, species and varieties — how are gemstones related?
Emerald and aquamarine look very different, yet belong to the same mineral species. Ruby and sapphire share the same basic structure, while garnet describes a group of minerals rather than a single mineral.
To understand these relationships, it helps to distinguish three terms: Group, Species and Variety. “Family” is often a convenient way to describe related gemstones, but is not a uniform rank in mineral classification.
Group, species and variety — what is the difference?
A group contains several mineral species related through their chemical composition and crystal structure. Tourmaline, garnet and feldspar are examples.
A mineral species is defined by its chemical composition and crystal structure. Quartz, beryl and corundum are mineral species.
A variety is a name given to some stones within a species, usually because of their color, appearance or optical phenomenon. Emerald and aquamarine are varieties of beryl; amethyst and citrine are varieties of quartz.
So “gemstone families” may refer either to groups containing several species or to different varieties of a single species.
Quartz — from amethyst to agate
Quartz is one of the most common minerals in Earth’s crust. It is silicon dioxide and has a Mohs hardness of 7.
- Amethyst — purple quartz.
- Citrine — yellow to orange quartz.
- Smoky quartz — smoky shades from light to very dark brown.
- Rose quartz — pink quartz, usually milky or translucent.
- Rock crystal — transparent, colorless quartz.
- Prasiolite — green quartz.
Alongside stones with relatively large crystals, some quartz materials consist of tiny crystals. Chalcedony is an example; familiar varieties include carnelian, chrysoprase and agate. Differences in structure, color and transparency create a remarkable range, despite a shared principal mineral component.
Beryl — emerald, aquamarine and more
Beryl is a mineral species containing beryllium and aluminum. Its Mohs hardness is 7.5–8.
- Emerald — green beryl colored by chromium, vanadium or both.
- Aquamarine — blue to greenish-blue beryl.
- Morganite — pink to peach beryl.
- Heliodor — yellow to greenish-yellow beryl.
- Goshenite — colorless beryl.
- Red beryl — a very rare variety, also known by the historical name Bixbite. “Red beryl” is preferred today to avoid confusion with the mineral bixbyite.
- Maxixe — deep-blue beryl with a different color mechanism from aquamarine. Its color can fade with exposure to light or heat.
Related stones are not identical in clarity, practical durability or price. Emerald, for example, often contains more inclusions and fractures than aquamarine and requires a different approach during setting. Belonging to the same species does not guarantee the same behavior in jewelry.
Corundum — ruby and sapphire
Corundum is aluminum oxide, with a Mohs hardness of 9. Ruby is red corundum; sapphire includes its other colors, such as blue, pink, yellow, green, purple, orange and colorless.
The boundary between pinkish-red ruby and pink sapphire is not always sharp, and laboratories and markets can differ in how they describe borderline stones.
Trace elements influence color. Chromium is associated with ruby’s red and the pink of some sapphires; iron and titanium play a central role in blue sapphire. Some stones also display a star or change color between different kinds of lighting.
Feldspar — a group of light and color effects
Feldspar, called פצלת השדה in Hebrew, is a large mineral group and one of the most common components of rocks in Earth’s crust. It includes several species and compositional series, such as orthoclase, microcline and the plagioclase minerals.
- Moonstone — known for a glow that seems to move inside the stone.
- Labradorite — can show strong flashes of color, often blue, green and gold.
- Sunstone — some stones show glitter caused by reflective inclusions.
- Amazonite — a blue-green variety of microcline.
A trade name does not necessarily identify a mineral species. “Rainbow moonstone,” for example, is usually transparent or pale labradorite rather than the material sold as classic moonstone.
Feldspar gemstones have a hardness of about 6–6.5, and many have cleavage — a tendency to break along specific planes in the crystal. Suitability for jewelry therefore depends on more than hardness alone.
Tourmaline — a group with enormous variety
Tourmaline is a group of mineral species with similar structures and different chemical compositions, including elbaite, dravite and schorl. Many transparent tourmalines used in jewelry are elbaite, but “tourmaline” does not identify one species.
- Rubellite — pinkish-red to red tourmaline.
- Indicolite — blue tourmaline.
- Verdelite — green tourmaline.
- Watermelon tourmaline — pink and green zones in the same stone.
Paraíba tourmaline is especially notable for vivid blue, turquoise and green colors, often described as “neon.” Copper plays a central role in its characteristic color.
The name comes from the Brazilian state of Paraíba, where the stones that gave it its name were discovered. However, the name does not guarantee Brazilian origin: it also applies to stones from other sources that meet the appropriate gemological definition. Not every blue or turquoise tourmaline is Paraíba — identification depends on chemical composition as well as appearance.
Tourmaline can contain several colors in one crystal. Viewing direction also affects color, making cutting orientation important. Its Mohs hardness is generally 7–7.5.
Garnet — much more than red
Garnet is a group of minerals with similar crystal structures. Although associated with red, garnets also occur in green, orange, yellow, pink and other colors.
Its principal species include pyrope, almandine, spessartine, grossular, andradite and uvarovite. Many stones combine components of several species rather than having the composition of only one.
Rhodolite combines mainly pyrope and almandine components. Tsavorite is green grossular, while demantoid is green andradite.
Composition affects color, optical properties and durability. Hardness is approximately 6.5–7.5, depending on species and composition.
Spinel — both a species and a group name
Spinel is the name of a broad mineral group and also of the mineral species that forms the familiar gemstone. Gem spinel occurs in red, pink, blue, purple, gray and other colors and has a Mohs hardness of 8.
Some important red spinels were historically identified as rubies because their colors were similar and modern identification tools were unavailable. Similar appearance does not make them the same mineral: spinel and ruby differ in composition and crystal structure.
Zoisite — tanzanite and its relatives
Zoisite is a mineral species in the epidote group. Tanzanite is its blue-violet variety, and thulite is pink zoisite.
Ruby in zoisite combines ruby with green zoisite-rich rock. It is a combination of different materials, rather than a ruby variety — a reminder that a gemstone’s trade name can describe a mixture of minerals.
Does every gemstone have a family of varieties?
Not every gemstone has as many variety names as quartz or beryl. Topaz is a mineral species in its own right, with different colors and trade names. Diamond is a mineral species made of carbon and can be colorless or colored.
Some jewelry materials are not a single mineral: lapis lazuli is a rock containing several minerals, amber is fossilized resin, and pearl forms through a biological process. “Gemstone” is therefore a broader term than “mineral.”
Why does this matter when choosing jewelry?
A name tells us something about a stone, but is not enough to choose it. Two stones of the same species can differ greatly in color, clarity, cutting, treatments and price. Even stones with similar hardness can respond differently to impact or pressure during setting.
Knowing the species and variety helps us understand what we see, which properties to examine and how to incorporate a stone into jewelry.
At TzurGems Jewelry & Gemstones, we combine Guy’s gemological knowledge with the craftsmanship of Rafael, an artist goldsmith, to select a stone suited to the design, its intended use and the person who will wear it.