Ruby in Zoisite

Description

Ruby in Zoisite, also known as Anyolite, is a striking metamorphic rock composed primarily of green zoisite, opaque red ruby (a variety of corundum), and often black amphibole (typically pargasite or hornblende). The vibrant green zoisite provides a stark contrast to the deep red ruby crystals, making it a visually appealing material. The ruby crystals are typically opaque and can range from small inclusions to larger, well-formed hexagonal prisms. The black amphibole often appears as irregular patches or streaks within the green zoisite matrix. It is not a single mineral but a rock assemblage.

How to Identify

Color

Dominantly green (zoisite) with prominent opaque red (ruby) inclusions and often black (amphibole) patches.

Luster

Zoisite: Vitreous to pearly; Ruby: Adamantine to vitreous; Amphibole: Vitreous to dull.

Texture

Granular to massive, often with visible individual crystals of ruby and amphibole embedded in the zoisite matrix.

Crystal Form

Ruby typically occurs as hexagonal prisms or irregular grains. Zoisite forms prismatic crystals, often massive. Amphibole forms acicular to prismatic crystals or irregular masses.

Cleavage

Zoisite: Perfect on {010}; Ruby: None (parting on {0001} and {1011}); Amphibole: Two distinct cleavages at approximately 56° and 124°.

Geological Environment

Medium to high-grade regional metamorphic terrains, particularly in areas where chromium-rich protoliths (e.g., anorthosites, gabbros, or ultramafic rocks) have undergone metasomatism or metamorphism.

Key Facts

• Hardness: Varies depending on the constituent minerals: Ruby (9), Zoisite (6-7), Amphibole (5-6). Overall rock hardness is intermediate.
• Specific Gravity: Varies: Ruby (3.97-4.05), Zoisite (3.10-3.38), Amphibole (2.9-3.6). The rock's specific gravity will be an average of its components.
• Crystal System: Ruby (Hexagonal), Zoisite (Orthorhombic), Amphibole (Monoclinic)
• Color: Green (zoisite), Red (ruby), Black (amphibole)
• Luster: Vitreous to pearly (zoisite), Adamantine to vitreous (ruby), Vitreous to dull (amphibole)
• Transparency: Ruby (Opaque in this form), Zoisite (Translucent to opaque), Amphibole (Opaque)
• Fracture: Ruby (Conchoidal to uneven), Zoisite (Uneven to conchoidal), Amphibole (Uneven to subconchoidal)
• Cleavage: Ruby (None, but parting), Zoisite (Perfect on {010}), Amphibole (Two distinct cleavages at ~56° and ~124°)
• Composition: A rock composed of the minerals Ruby (Al2O3), Zoisite (Ca2Al3(SiO4)3(OH)), and various amphiboles (e.g., Pargasite, Hornblende - complex silicates).

Quick Check

• Color: Green with red and black inclusions
• Luster: Vitreous to pearly (zoisite), adamantine to vitreous (ruby)
• Streak: White (for zoisite and ruby), greenish-white to gray (for amphibole)

Physical Characteristics

• Crystal Habit: Ruby: Hexagonal prisms, granular; Zoisite: Prismatic, massive; Amphibole: Acicular, prismatic, massive.
• Cleavage Type: Zoisite: Perfect basal; Ruby: Parting, not true cleavage; Amphibole: Prismatic.
• Fracture Type: Conchoidal to uneven for ruby and zoisite, uneven to subconchoidal for amphibole.
• Tenacity: Brittle for all constituent minerals.
• Luster Type: Vitreous to pearly for zoisite, adamantine to vitreous for ruby, vitreous to dull for amphibole.

Formation

Ruby in Zoisite forms through regional metamorphism of chromium-rich igneous rocks (like anorthosite or gabbro) or sedimentary rocks (like bauxite) that have been subjected to high pressures and temperatures. The chromium content is essential for the red color of ruby, while the presence of aluminum, calcium, and silicon under specific metamorphic conditions leads to the formation of zoisite. The green zoisite often forms from the alteration of plagioclase feldspar, while the black amphibole (often pargasite or hornblende) is a common accessory mineral.

Usage

Primarily used as an ornamental stone, for carvings, cabochons, spheres, and decorative objects. It is also popular in lapidary arts and as a collector's specimen. Due to its striking color contrast, it is highly valued for aesthetic purposes.

Age Distribution

Precambrian to Cenozoic, depending on the specific metamorphic event and protolith age.

Where to Find

Finding Tips

Similar Rocks

Scientific Classification

Mineral Class

Oxide (Ruby), Sorosilicate (Zoisite), Inosilicate (Amphibole)

Group

Corundum Group (Ruby), Epidote Group (Zoisite), Amphibole Group (Amphibole)

Crystal System

Hexagonal (Ruby), Orthorhombic (Zoisite), Monoclinic (Amphibole)

Chemical Formula

Ruby: Al2O3; Zoisite: Ca2Al3(SiO4)3(OH); Amphibole: Complex silicates, e.g., Pargasite: NaCa2(Mg4Al)Si6Al2O22(OH)2

Composition

Aluminum oxide (Ruby), Calcium aluminum silicate hydroxide (Zoisite), Complex calcium magnesium iron aluminum silicates (Amphibole).

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