Both are common alteration products of magnesian silicate minerals such as olivine, pyroxene, and amphibole.
Pargasite, pr′ga-sīt, n. a dark-green crystallised variety of amphibole or hornblende.
The fibrous variety of serpentine is the principal source of asbestos, an amphibole asbestos being less common.
Any of a large group of usually dark minerals composed of a silicate joined to various metals, such as magnesium, iron, calcium or sodium. Amphiboles occur as columnar or fibrous prismatic crystals in igneous and metamorphic rocks. Most are monoclinic, but some are orthorhombic. Hornblende, actinolite and glaucophane are amphiboles. Chemical formula: (Mg,Fe,Ca,Na)2-3(Mg,Fe,Al)5(Si,Al)8O22OH2.