As the oceanic crust subducts, it experiences a very high pressure but relatively low temperature style of regional metamorphism, and the basalt and gabbro are transformed to blueschist (or glaucophane
schist) and then to eclogite (Figure 5).
It consists of metagabroic rocks, garnet amphibolites, amphibole schists, quartz-sericite schists and quartzites of medium- to low-pressure, as well as lawsonite and glaucophane
schists and eclogites of high pressure and serpentinized ultramafic rocks (Maya and Gonzalez, 1995).
The phosphorites are of pelletal type and commonly contain cellophane, dahlite, francolite, glaucophane
, dolomite, iron oxide and pyrite in various proportions.
(1982): Presence de glaucophane
detritique dans le Maastrichtien inferieur de Sardaigne orientale.
Beryl is accompanied by garnet, glaucophane
, quartz, epidote, muscovite and chlorite in the stream sediments.
For example, during the Neolithic, polished axes and chisels were made from greenschists and glaucophane
schists in northern Italy (D'Amico 2005) and from glaucophane
schists in the western Provence region of southern France (Ricq-de Bouard and Fedele 1993).
The crystals line seams in a hard, dark glaucophane
schist from which the original calcite seam-fillings have been dissolved away.
Diamondiferous zones are characterised by dynamic and thermal metamorphism and the presence of grossular garnets, glaucophane
and other minerals of high-pressure zones.
Jitang metamorphic complexes: 40Ar/39Ar age of Phengite in Mica-quartzose Schist 230+-1 Ma (Wang GH, 2008); Gemuri metamorphic complexes: Ar-Ar age of Glaucophane
222Ma, Crossite 223-220Ma or 221Ma, and Phengite 215Ma (Table 1); Jitang metamorphic complexes in this study: 40Ar/39Ar ages of Phengite in Mica-quartzose Schist 219.1+-1, 218.1+-1.3, 228.8+-1.2, 228+-1.3 Ma et al.