Amphibole Minerals: Structure and Types

Amphibole Minerals Overview

• Amphibole minerals are present in igneous and metamorphic rocks.
• Form needle-like or prism-shaped crystals, with most not classified as asbestos.
• Asbestos belongs to the amphibole mineral group but is not representative of all amphiboles.

Classification and Structure

• Amphiboles are classified as inosilicates, featuring double chains, unlike pyroxenes, which are single chain silicates.
• Common in continental regions due to weathering, whereas pyroxenes are typical in mid-ocean ridge basalt (MORB).
• Crystal structure includes chains extending parallel to the c axis, stacked alternately with points facing each other.

Occurrences in Rocks

• Found in intrusive igneous rocks: granodiorite, diorite, granite.
• Present in extrusive igneous rocks: rhyolite, dacite, and andesite.
• Found in metamorphic rocks such as amphibolite, schist, and gneiss; can form long, thin crystals.

Greenstone Belts

• Greenstone belts are characterized by green amphibole and consist of metamorphosed igneous and sedimentary rock.

Asbestos

• Most commercial asbestos derived from chrysotile, a fibrous variety of serpentine.
• Historically used for insulation and roofing materials due to heat and fire resistance.
• Global asbestos removal efforts are underway due to safety concerns.

Decorative Uses

• Amphiboles enhance the decorative patterns of various building stones.
• Jade, prized in multiple cultures (Chinese, Maori, Aztec), consists of amphibole or pyroxene.
• Nephrite (amphibole) and jadeite (pyroxene) are nearly indistinguishable from one another.