Amphibole or Amphibole — Rolled

Amphibole is a group of double-chain silicates with the general formula (Ca,Na,K)₂₋₃(Mg,Fe,Al)₅(Al,Si)₈O₂₂(OH,F)₂, encompassing several mineral species such as hornblende, actinolite, tremolite and riebeckite. It forms predominantly in medium to high-grade igneous and metamorphic rocks, such as amphibolites, gneisses and schists, in addition to occurring in plutonic rocks such as granites and diorites. The color varies between dark green, black, brown and grayish blue, determined by the specific chemical composition of each species in the group — the concentration of iron, magnesium, calcium and aluminum in the crystalline structure defines both the tone and the mineral variety present. It presents characteristic prismatic cleavage in two planes with an angle of approximately 120°, a diagnostic property that distinguishes the group of amphiboles from pyroxenes. The mechanical rolling process progressively rounds the ends and corners of the parts, resulting in a smoothed external profile. Hardness: 5 to 6 on the Mohs scale. Density: 2.9 to 3.6 g/cm³. Crystalline system: monoclinic to orthorhombic. Available variations, approximate data: Size: 3 to 9 cm Unit weight: up to 250 g (approx.) Average: 10 to 20 pieces per kg (approx.)