PETROGRAFI BATUAN METAMORF

OLEH :

AGUS HENDRATNO

Laboratorium Geologi OptikJurusan Teknik Geologi

Fakultas TeknikUniversitas Gadjah Mada

Yogyakarta

Quartz metamorf

As deformation increases, the quartz grains are stretched outparallel to the direction of flow in the rock. Crossed polarizerswith gypsum plate. Protomylonite, JŠmtland County, Sweden

Glaucophane

Note the anomalous blue-gray interference colors in theglaucophane in this slide.

Sillimanite

The slender prismatic crystals show high relief and are colourless in plane polarizedlight (left). Note the parallel extinction of one of the crystals and the end on view ofanother. Birefringence is usually first order, however, lower second order coloursmay be seen (in crossed polars).

Tourmaline

This slide shows zoned trigonal cross-sections and elongate sections anddisplaying maximum birefringence (x-nicol). Note green to brown pleochroism.Tourmaline may also display bluish pleochroism.. The matrix is quartz.

Eclogite

Garnet and clinopyroxene are the two major minerals in eclogite. Eclogite isbasalt which has been metamorphosed at very high pressures insubduction zones.

Eclogite

Garnet and clinopyroxene are the two major minerals in eclogite. Eclogite isbasalt which has been metamorphosed at very high pressures insubduction zones.

Foliation

A foliation is any planar fabric in a metamorphic rock. In this case, the foliationis defined by aligned sheets of muscovite sandwiched between quartz grains.

Gneiss

This is a sample of the famous Lewisian Gneiss. Note the sutured grainboundaries between quartz. This rock also contains plagioclase, biotite, and K-feldspar.

Granoblastic texture

Note how the interlockingplagioclase grains in this rock meetat ~120 degree triple junctions. Thisfeature is characteristic ofgranoblastic texture.

Note how the interlocking calcitegrains in this rock meet at ~120degree triple junctions. This featureis characteristic of granoblastictexture.

Biotite hornfels

Hornfels is a fine-grained contact metamorphosed rock. The layers of biotite inthis sample probably respresent original sedimentary bedding.

Spotted hornfels

A hornfels is a fine-grained contact-metamorphosed rock. The mineralresponsible for the spots is probably cordierite or andalusite.

Marble

Note the dominance of calcite in this rock.

Mesh texture

Serpentine is surrounding and veining relict clinopyroxenein this low grade meta-mafic rock.

Mylonite

Note the extremely fine grain size and strong foliation in thismylonite. These features were probably caused by intenseshearing.

Porphyroclastic texture

This large grain is a K-feldspar porphyroclast. Unlike porphyroblasts,porphyroclasts are not grown in-situ, but rather are fragments of pre-existingminerals which were broken up during the process of metamorphism.

Palisades texture

The region of coarser-grained quartz in the upper center portion of thisphotomicrograph was probably originally occopied by coesite, the high-pressure polymorph of quartz.

Phyllite

This is a sample of the Ira Phyllite. Note the wavy foliationand the overall fine-grain size of this rock.

Poikiloblastic texture

Poikiloblastic texture describes porphyroblasts which are riddled with finergrained inclusions of other minerals. Here, orange tourmaline and gray K-feldspar include numerous, fine- grained quartz and muscovite mica grains.

Poikiloblastic texture

This is an andalusite porphyroblast with poikiloblastic texture. The foliation(oriented roughly N-S in this view) is wrapped around the left and right corners ofthis grain, suggesting synkinematic growth of the andalusite porphyroblast

Quartzite

Note the sutured grain boundaries between the quartzgrains in this rock.

Slate

Note the fine grain size and the unimpressive foliation inthis weakly-metamorphosed rock.

Sub-grain in quartz

The crystal structure of this quartz grain has been deformed(probably by low-grade metamorphism) to produce sub-grains.

Whiteschist

This is a photomicrograph of a high-pressure schist from the famour Dora Mairamassif in Italy. The region of coarser-grained quartz in the upper center portion ofthis photomicrograph was probably originally occopied by coesite, the high-pressure polymorph of quartz.

Talc-tremolite schist

Talc forms the fine-grained matrix between the prismaticcrystals of tremolite in this rock. Note the ~120 degreecleavages in some of the tremolite sections.