Turquoise and Ruby

Mineral

Turquoise (CuAl6(PO4)4(OH)8·4H2O) and Ruby (Al2O3:Cr)

Also known as: Turquoise: Callais, Agaphite; Ruby: Corundum (red variety)

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Description

Turquoise is an opaque, hydrous phosphate of copper and aluminum, known for its distinctive blue-green to sky-blue color. It often forms in veins, nodules, and crusts. Ruby is a transparent to translucent red variety of the mineral corundum (aluminum oxide), with its characteristic red color derived from trace amounts of chromium. It is one of the hardest natural minerals, second only to diamond.

How to Identify

Color: Turquoise: Sky-blue, blue-green, apple-green. Ruby: Red, purplish-red, orangey-red.
Luster: Turquoise: Waxy to subvitreous. Ruby: Adamantine to vitreous.
Texture: Turquoise: Typically massive, cryptocrystalline, often with a fine-grained, porous texture. Ruby: Crystalline, often prismatic or tabular, sometimes granular.
Crystal Form: Turquoise: Rarely forms distinct crystals; usually massive, botryoidal, reniform, or stalactitic. Ruby: Hexagonal system, typically forming prismatic, tabular, or bipyramidal crystals. Often found as irregular grains or masses.
Cleavage: Turquoise: Perfect on {001} (rarely observed due to cryptocrystalline nature). Ruby: No true cleavage, but exhibits parting on {0001} and {1011} due to lamellar twinning.
Geological Environment: Turquoise: Secondary mineral in weathered, aluminum-rich igneous rocks (e.g., porphyries, rhyolites) in arid regions, often associated with limonite, kaolinite, and chalcedony. Ruby: Metamorphic rocks (marble, gneiss, schist) and some igneous rocks (basalt, syenite) associated with other corundum varieties, spinel, garnet, and mica.

Key Facts

Hardness: Turquoise: 5-6 (Mohs); Ruby: 9 (Mohs)
Specific Gravity: Turquoise: 2.60-2.90; Ruby: 3.97-4.05
Crystal System: Turquoise: Triclinic; Ruby: Hexagonal (Trigonal)
Color: Turquoise: Sky-blue, blue-green, apple-green; Ruby: Red, purplish-red, orangey-red
Luster: Turquoise: Waxy to subvitreous; Ruby: Adamantine to vitreous
Transparency: Turquoise: Opaque, rarely semi-translucent; Ruby: Transparent to translucent
Fracture: Turquoise: Conchoidal to uneven; Ruby: Conchoidal to uneven
Cleavage: Turquoise: Perfect on {001} (rarely observed); Ruby: None, but parting on {0001} and {1011}
Composition: Turquoise: Hydrous copper aluminum phosphate; Ruby: Aluminum oxide with chromium impurity

Quick Check

Color: Turquoise: Blue to green; Ruby: Red
Luster: Turquoise: Waxy to subvitreous; Ruby: Adamantine to vitreous
Streak: Turquoise: White to pale blue-green; Ruby: White

Physical Characteristics

Crystal Habit: Turquoise: Massive, cryptocrystalline, botryoidal, reniform, stalactitic; rarely small, distinct crystals. Ruby: Prismatic, tabular, bipyramidal, rhombohedral; often granular or massive.
Cleavage Type: Turquoise: Perfect on {001} (rarely seen); Ruby: None, but parting on {0001} and {1011}.
Fracture Type: Turquoise: Conchoidal to uneven; Ruby: Conchoidal to uneven.
Tenacity: Turquoise: Brittle; Ruby: Brittle.
Luster Type: Turquoise: Waxy to subvitreous; Ruby: Adamantine to vitreous.

Formation

Turquoise: A secondary mineral formed by the alteration of aluminum-rich igneous rocks in arid climates, where copper-bearing solutions react with phosphate and aluminum. Ruby: Forms in metamorphic rocks (e.g., marble, gneiss, schist) and some igneous rocks (e.g., basalt, syenite) under high temperature and pressure conditions, with chromium substituting for aluminum in the corundum lattice.

Usage

Both are highly prized gemstones. Turquoise is used extensively in jewelry, ornamental carvings, and as an inlay material. Ruby is one of the 'Big Three' colored gemstones, used in high-end jewelry, watches, and as a laser medium (synthetic ruby).

Age Distribution

Turquoise: Typically Cenozoic, forming in arid regions. Ruby: Precambrian to Cenozoic, depending on geological setting.

Where to Find

Turquoise: Southwestern United States (Arizona, Nevada, New Mexico)

Historically significant deposits, particularly in Arizona (e.g., Sleeping Beauty, Kingman mines) and Nevada (e.g., Lander Blue, Lone Mountain).

Turquoise: Iran (Persia)

Nishapur district, known for its high-quality 'Persian Blue' turquoise.

Turquoise: China (Hubei province)

Significant producer of turquoise, often with a greener hue.

Turquoise: Egypt (Sinai Peninsula)

Ancient mines, particularly Serabit el-Khadim and Wadi Maghareh.

Ruby: Myanmar (Burma)

Mogok Valley is world-renowned for its 'Pigeon's Blood' rubies, found in marble deposits.

Ruby: Thailand/Cambodia

Historically important sources, often producing darker, brownish-red rubies from basaltic host rocks.

Ruby: Sri Lanka

Known for a variety of corundum colors, including rubies, often found in alluvial deposits.

Ruby: Mozambique

Emerging as a major source, particularly the Montepuez deposit, producing high-quality rubies.

Ruby: Afghanistan, Pakistan, Vietnam, Tanzania, Madagascar

Other notable sources with varying qualities and geological settings.

Finding Tips

Turquoise Prospecting

Look for areas with altered igneous rocks, especially in arid environments. Turquoise often occurs in veins or nodules within limonite-stained host rock. Surface indications can include greenish or bluish stains on rocks.

Ruby Prospecting

Search in metamorphic terrains, particularly marble, gneiss, or schist, or in alluvial deposits downstream from such formations. Rubies are dense and will concentrate in placers. Look for associated minerals like spinel, garnet, and mica.

Safety Precautions (General)

Always obtain permission before collecting on private land. Be aware of local regulations for public lands. Wear appropriate safety gear, including eye protection and gloves, especially when breaking rocks. For turquoise, avoid inhaling dust if cutting or polishing, as fine particulate matter can be a respiratory irritant. For ruby, no specific chemical hazards are associated with handling the mineral itself, but standard rock collecting safety applies.

Distinguishing Features (Turquoise)

Its unique blue-green color, waxy luster, and relative softness (Mohs 5-6) help distinguish it. Variscite is typically greener and has a lower specific gravity. Chrysocolla is softer and often more gelatinous. Azurite is a deeper blue and effervesces with acid.

Distinguishing Features (Ruby)

Its intense red color, high hardness (Mohs 9), and adamantine luster are key. Red garnet is softer (Mohs 6.5-7.5), has a different crystal habit, and often shows conchoidal fracture. Red spinel is also hard (Mohs 8) but is singly refractive (isotropic) compared to ruby's double refraction (anisotropic). Red tourmaline is softer (Mohs 7-7.5) and has distinct striations on its crystal faces.

Similar Rocks

Chrysocolla

Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O (x<1)

Also known as: Copper silicate

Variscite

AlPO4·2H2O

Also known as: Utahlite

Azurite

Cu3(CO3)2(OH)2

Also known as: Chessylite

Garnet (Pyrope/Almandine)

Mg3Al2(SiO4)3 / Fe3Al2(SiO4)3

Also known as: Red Garnet

Spinel (Red)

MgAl2O4

Also known as: Balas Ruby

Red Tourmaline (Rubellite)

Complex borosilicate

Also known as: Rubellite

Scientific Classification

Mineral Class: Turquoise: Phosphate mineral; Ruby: Oxide mineral
Group: Turquoise: Turquoise group; Ruby: Corundum group
Crystal System: Turquoise: Triclinic; Ruby: Hexagonal (Trigonal)
Chemical Formula: Turquoise: CuAl6(PO4)4(OH)8·4H2O; Ruby: Al2O3:Cr
Composition: Turquoise: Copper aluminum phosphate with water; Ruby: Aluminum oxide with trace chromium

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