Crystal System: Monoclinic Status of Occurrence: Confirmed
Occurrence Chemical Composition: Calcium magnesium iron silicate
hydroxide Chemical Formula: Ca2(Mg,Fe2+)5Si8O22(OH)2 Method(s)
of Verification: Moel Hebog - X-ray diffraction (Langford,
1973); various other localities - EMPA (Bevins & Rowbotham,
1983; Gibbons & Gyopari, 1986; Bevins & Merriman, 1988). -
Metamorphic: low-grade Introduction: actinolite is a member of
the amphibole group. It forms a series with tremolite and ferro-
actinolite being more iron-rich than the former. It occurs in
basic rocks metamorphosed under low-grade metamorphic conditions
(greenschist and blueschist facies). Occurrence in Wales:
actinolite has a widespread distribution across Wales in altered
basic igneous rocks, although in most instances it can only be
identified with the aid of a petrological microscope. Greater
access to electron microscope analyses has made it easier to
differentiate actinolite from ferro-actinolite. Early reported
occurrences include those by Gree