Ruby in Fuchsite

Description

Ruby in Fuchsite is a striking metamorphic rock composed primarily of green fuchsite (a chromium-rich variety of muscovite mica) with embedded, often opaque, red crystals of corundum (ruby). The vibrant green matrix provides a stark contrast to the deep red ruby inclusions, making it a highly sought-after ornamental stone. The fuchsite gives the rock a characteristic shimmering or sparkly appearance due to its micaceous nature. Other accessory minerals like kyanite, rutile, and chlorite may also be present.

How to Identify

Color

Dominantly green (fuchsite) with distinct red (ruby) inclusions. The green can range from pale to deep emerald green, often with a silvery sheen. The red rubies are typically opaque and can vary from pinkish-red to deep crimson.

Luster

Fuchsite exhibits a pearly to vitreous luster, often with a shimmering or metallic sheen due to its micaceous nature. Ruby inclusions are typically dull to sub-adamantine.

Texture

Schistose texture, meaning it has a foliated or layered appearance due to the alignment of mica flakes. The ruby crystals are often granular or blocky, embedded within the micaceous matrix.

Crystal Form

Fuchsite occurs as small, platy, hexagonal crystals, often intergrown to form a micaceous mass. Ruby (corundum) typically forms hexagonal prisms or barrel-shaped crystals, often anhedral (lacking well-formed faces) within the matrix.

Cleavage

Fuchsite (muscovite) has perfect basal cleavage in one direction, allowing it to split into thin, flexible sheets. Ruby (corundum) has no true cleavage but exhibits parting along rhombohedral planes.

Geological Environment

Found in regionally metamorphosed terrains, particularly in areas where ultramafic rocks (e.g., serpentinites, peridotites) or chromium-rich sediments have undergone medium to high-grade metamorphism. It is often associated with greenstone belts and ancient cratons.

Key Facts

• Hardness: Fuchsite: 2.5-3 (Mohs); Ruby: 9 (Mohs)
• Specific Gravity: Fuchsite: 2.77-2.88; Ruby: 3.97-4.05
• Crystal System: Fuchsite: Monoclinic; Ruby: Trigonal
• Color: Green (fuchsite), Red (ruby)
• Luster: Pearly to vitreous (fuchsite), Dull to sub-adamantine (ruby)
• Transparency: Fuchsite: Translucent to opaque; Ruby: Opaque (in this context)
• Fracture: Fuchsite: Uneven to splintery; Ruby: Conchoidal to uneven
• Cleavage: Fuchsite: Perfect basal cleavage (001); Ruby: No true cleavage, but parting on {1011} and {0001}
• Composition: Fuchsite: K(Al,Cr)2(AlSi3O10)(OH)2; Ruby: Al2O3 (with Cr3+ impurities)

Quick Check

• Color: Green with red inclusions
• Luster: Pearly to vitreous (fuchsite), dull to sub-adamantine (ruby)
• Streak: White (fuchsite), colorless (ruby)

Physical Characteristics

• Crystal Habit: Fuchsite: Micaceous, platy, foliated; Ruby: Granular, anhedral to subhedral hexagonal prisms
• Cleavage Type: Fuchsite: Perfect basal; Ruby: Parting
• Fracture Type: Fuchsite: Uneven to splintery; Ruby: Conchoidal to uneven
• Tenacity: Fuchsite: Flexible, elastic; Ruby: Brittle
• Luster Type: Fuchsite: Pearly to vitreous; Ruby: Dull to sub-adamantine

Formation

Ruby in Fuchsite forms during regional metamorphism of ultramafic rocks (rich in chromium) or aluminum-rich sediments that have been metasomatically altered. The chromium content in the protolith is crucial for the formation of both the red ruby (Cr-rich corundum) and the green fuchsite (Cr-rich muscovite). The metamorphic conditions typically involve medium to high temperatures and pressures, leading to the recrystallization of existing minerals and the growth of new ones. The ruby crystals are often porphyroblastic, meaning they grew larger than the surrounding matrix minerals.

Usage

Primarily used as an ornamental stone, for carving, cabochons, spheres, and decorative objects. It is also popular in lapidary arts due to its striking color contrast. While the ruby inclusions are genuine corundum, they are typically opaque and not of gem quality for faceting.

Age Distribution

Typically Precambrian to Paleozoic, formed during regional metamorphism.

Where to Find

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Scientific Classification

Mineral Class

Silicate (Fuchsite), Oxide (Corundum)

Group

Mica Group (Fuchsite), Corundum Group (Ruby)

Crystal System

Monoclinic (Fuchsite), Trigonal (Ruby)

Chemical Formula

K(Al,Cr)2(AlSi3O10)(OH)2 (Fuchsite); Al2O3 (Ruby)

Composition

Hydrous potassium aluminum chromium silicate (Fuchsite); Aluminum oxide with chromium impurities (Ruby)

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