!GLG 101-Illustrated Vocabulary-Chapter7
!Metamorphic Minerals and Rocks
copyright 2003-Roger Weller
!chill zone
*the outer part of a magma body that cools quicker because it is in contact with the cooler
country rock; consequently grain sizes in this region are smaller than for the rest of the
magma body.
!compression
*a squeezing force that tends to flatten an object.
!contact metamorphism
*a form of metamorphism where rocks are baked by the heat from an igneous intrusion.
!country rock
*the pre-existing rock that into which a magmatic intrusion invades.
!epidote
*a pistachio or pea soup green silicate mineral; often found in a massive state as a coating
on fault surfaces.
*[Mt. Whitney-Fault Surface with Epidote-Close Up]
!fissility
*the property of a rock, such as shale or slate, of splitting into thin layers
!foliation
*the layering of flat minerals, usually mica, in metamorphic rocks such as schist and
gneiss.
*[Mica Schist-1]
*[Gneiss-cut- #2]
!garnet
*A silicate mineral family that forms somewhat rounded crystals in the isometric system.
Common shapes are dodecahedrons (12 sided) and trapezohedrons (24 sided).
Depending upon its quality, this mineral can be used either for abrasives (sandpaper) or
gemstones (usually red).
*[Garnet in Schist]
*[Garnet-Trapezohedron]
!hornfels
*a non-foliated metamorphic rock commonly produced by the baking of shale or basalt
by the heat from a nearby igneous intrusion.
*[Hornfels-1]
!jade
*also known as nephrite jade; a variety of amphibole.
*[Jade-Pebble]
*[Jade-White and Green]
!jadeite
*sometimes called jadeite jade; a variety of pyroxene.
*[Jadeite, Bracelets]
*[Jadeite Carving-1]
!kyanite
*a metamorphic mineral that forms flat, blade-like blue crystals.
*[Kyanite]
!lineation
*elongated minerals within a metamorphic rock are aligned in the same direction; often
seen in gneisses.
*[Gneiss-Lineation-1]
*[Gneiss-Lineation-2]
!marble
*a metamorphic rock formed from limestone or dolomite that has been recrystallized.
The most commonly identified form of this material is white with gray streaks, but over
300 varieties of different colors and patterns have been recognized.
*[Marble-polished-breccia #1]
*[Marble-polished-swirl pattern #3]
!metaconglomerate
*a metamorphosed conglomerate. Often identified by the presence of elongated and
parallelly aligned pebbles.
!metamorphic rock
*a rock that has been altered from its original condition by heat and/or pressure.
*[Slate-1]
*[Mica Schist-4]
*[Gneiss-2]
*[Marble-polished-swirl pattern #1]
!metamorphism
*the process of altering the chemistry and/or structure of a rock through heat and/or
pressure.
!mica schist
*a foliated metamorphic rock between phyllite and gneiss that is made up of sparkly,
small mica crystals.
*[Mica Schist-1]
*[Mica Schist-2]
!phyllite
*a foliated metamorphic rock between slate and schist; often has a silky appearance and a
slighly wavy surface.
*[Phyllite-1]
*[Phyllite-3]
!ptygmatic folds
*inticately folded veins found in granitic and metamorphic rocks.
*[Santa Catalinas-Ptygmatic Folds]
*[Santa Catalinas-Ptygmatic Folds in Xenolith Surrounded by Granite]
!quartzite
*the metamorphic rock that started out as a sandstone; consists of well cemented quartz
sand grains.
!regional metamorphism
*a large region has been metamorphosed due to a major tectonic event such as collision
of continents.
!schist
*a foliated metamorphic rock, more metamorphosed than phyllite, but less
metamorphosed than gneiss; often has a sparkly surface due to the reflection of light from
a myriad of tiny mica crystals.
*[Mica Schist-4]
*[Mica Schist-5]
!serpentine
*a non-foliated sedimentary rock ranging in color from yellow green to dark green to
nearly black; closely resembles jade but is far less durable.
*[Serpentine]
!shear
*the type of stress where one block slides past another block; materials caught between
the two blocks are said to be undergoing s
!skarn
*limestones or dolomites that have been silicified and mineralized with iron, magnesium,
and aluminum silicates as part of a metamo
!slate
*a metamorphic rock, often gray or black in color, that splits into vey flat sheets;
produced by the metamorphism of shale.
*[Slate-1]
!staurolite
*a brown-colored metamorphic silicate mineral that often forms interpenetration twins in
the form of crosses where the crystals can occur at 90 degrees or 60 degrees.
*[Staurolite-Crystals]
!talc
*a metamorphic mineral, typically white or pink, that is extremely soft. When ground to
a fine powder with some added perfume, it becomes talcum powder.
*[Talc-White]
!xenolith
*a baked inclusion of country rock surrounded by an intrusive igneous rock.
*[Mt. Whitney-Xenoliths-1]
*[Mt. Whitney-Xenolith-2]