Blueschist terranes are rare and contain rocks and minerals that you may be unfamiliar with. Fortunately, the department has a very good collection of blueschist rocks from Ile de Groix, France, which are similar to the rocks you will see in Syros. Examine the following hand specimens to familiarize yourself with the rocks and minerals you will see in the coming weeks. Bring a hand lens and the mineral identification table included in the mapping course writeup. The minerals are best examined in natural light close to the windows in the lab.

      The rocks are in the cabinet nearest to the fire extinguishers in the Level II lab, in the drawers labeled ``Ile de Groix.''

Drawer 1

IG13, IG14

Glaucophane epidote schist. Glaucophane is the blue, acicular mineral that forms the anastomosing lineation on the surface. Blocky rhombohedrons are pseudomorphs after lawsonite of greenish epidote. Brown-stained cavities probably mark sites of now-weathered carbonate, possibly ankerite (iron carbonate). IG14 contains red garnets.

IG35

Glaucophane epidote garnet schist. Note lineation formed by aligned glaucophane, and foliation formed by alternating glaucophane- and epidote-rich layers in original protolith. Pale red garnets and a large pale-green epidote porphyroblast on the narrower of the two flat, uncut surfaces. Epidote color deepens to green with increasing ferric iron substitution for aluminum.

IG52

White-mica chlorite schist. White mica is probably mixture of phengite (stable at high pressure) and muscovite (stable at low pressure). Soft-feeling surface on stroking suggests pyrophyllite or talc may also be present. Dark green chlorite interleaves the mica. Cut surface shows crenulation cleavage developed in the foliation.

IG GXT

Epidote albite white mica schist. Albite porphyroblasts in an epidote white-mica matrix. Epidote is pale, almost colorless but evident in porphyroblasts on the surfaces.

Drawer 2

IG3

Garnet muscovite glaucophane quartz schist. Brownish garnets prominent on weathered surface and cut face. Mica is probably muscovite because it forms large platy porphyroblasts - phengite is more brittle and forms in smaller, finely-disseminated masses. Matrix is quartz and muscovite and contains pale iron-poor glaucophane, evident on the cut surface. This rock is characteristic of the silicic units intercalated with the limestones throughout the field area in Greece.

IG29

Chloritoid muscovite garnet schist. Dark mineral in this rock is chloritoid rather than glaucophane - note absence of bluish color and more equant habit to contrast with acicular glaucophane. Brown garnets spread throughout sample. Minor epidote. Late quartz infill in foliation. Chloritoid layers are boudinaged in cut face bearing sample number. Sample is distinctly dense.

Drawer 3

IG I

Epidote eclogite. Abundant red-brown garnets and apple-green pyroxene indicates eclogite. Epidote and white mica (probably phengite on account of its association with omphacitic pyroxene and garnet, supported by it being small, disseminated porphyroblasts) are the other identifiable minerals in the specimen.

IG2, IG45

Glaucophane eclogite. Note characteristic dark color, density, garnets and an apple-green pyroxene. Garnet + omphacitic pyroxene make this an eclogite. There is a pronounced lineation in the glaucophanes even in this dark rock. Garnet cores are darker than rims, probably more iron-rich earlier in their growth phase. Garnets in IG45 have sigmoidal tails, indicating deformation during growth.

IG10

Glaucophane epidote garnet schist. Prominently lineated glaucophanes embedded in a matrix of sickly-green epidote. Minor garnet, rare chloritoid and traces of white mica (probably phengite) complete the identifiable minerals in the rock. Chloritoid distinguished from glaucophane by blacker appearance and blockier habit. Glaucophane forms a weak, chaotic foliation in the rock.

IG43

Glaucophane epidote garnet schist. Again, note rhomboidal epidote pseudomorphs after lawsonite. Some pseudomorphs also contain garnets. White mica probably phengite. Glaucophane is paler, more magnesian than other specimens described above.

Drawer 4

IG46

Ferrotremolite albite epidote schist. Ferrotremolite (actinolite) is darker green, epidote paler green. Albite porphyroblasts grew from protolith and now form crenulated foliation seen on the cut surface and on base of hand sample. Weathering of carbonate probably formed voids in sample. Minor, stained muscovite on outer surface.

Drawer 5

IG61

Glaucophane epidote garnet schist. Spectacular epidote pseudomorphs after lawsonite in a felty matrix of glaucophane. Note strong glaucophane lineation. Equant, fine-grained garnets form reddened areas on the hand sample's surface.