Aluminosilicates
Today
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Silicates (common in metamorphic rocks)
ƒ Aluminosilicates 3 polymorphs: Andalusite, Kyanite, Sillimanite
ƒ Phyllosilicates (Sheet silicates)
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Mica group – Biotite and Muscovite
Chlorite
Serpentine
Talc
Clay minerals
Garnet group – Almandine, Grossular, Pyrope, etc.
Staurolite
Epidote group
Idocrase (Vesuvianite)
Tourmaline
Beryl
Sphene
Topaz
Aluminosilicates
Andalusite (Al2SiO5)
Sillimanite
Kyanite
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Sillimanite (fibrous)
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Andalusite
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var. Chiastolite
http://mineral.galleries.com/minerals/silicate/andalusi/andalusi.htm
Kyanite (Al2SiO5)
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Color: Usually blue, but also can be white, gray or green. Color is
often not consistent throughout the crystal and can be blochy or in
streaks.
Luster: Vitreous to almost pearly.
Transparency: crystals are transparent to translucent.
Crystal System: Triclinic; bar 1
Crystal Habits: Flat, pinacoid dominated, prismatic crystals
(“blades”) often embedded in metamorphic rocks and quartz veins.
Cleavage: Good in one direction parallel to the flat pinacoid face.
Fracture: Splintery.
Hardness: Approximately 4.5 when scratched parallel to the long
axis of the crystal and approximately 6.5 when scratched
perpendicular to or across the long axis.
Specific Gravity: Approximately 3.58+ (above average)
Streak: White.
High P polymorph
http://mineral.galleries.com/minerals/silicate/kyanite/kyanite.htm
Color: White, red, brown, orange and green.
Luster: Vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System: Orthorhombic; 2/m2/m2/m
Crystal Habits: include prismatic crystals with a square
cross section terminated by a pinacoid. also massive and
granular. Var. Chiastolite: dark inclusions in the shape
of a “X”.
Cleavage: Good in two directions.
Fracture: Splintery to subconchoidal.
Hardness: 7.5 (harder than Quartz)
Specific Gravity: Approximately 3.15+ (above average)
Streak: White.
Low P polymorph
Sillimanite (Al2SiO5)
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Color: White, brown and green.
Luster: Silky when fiberous or vitreous otherwise.
Transparency: Crystals are transparent to translucent.
Crystal System: Orthorhombic; 2/m2/m2/m
Crystal Habits: Include rare prismatic crystals but
mostly fibrous masses.
Cleavage: Good in one direction lengthwise.
Fracture: Splintery.
Hardness: 7.5 in large crystals but more fiberous forms
are softer.
Specific Gravity: Approximately 3.2+ (above average)
Streak: White.
High T polymorph
http://mineral.galleries.com/minerals/silicate/silliman/silliman.htm
1
Staurolite
Staurolite (Fe2Al9Si4O22(OH)2)
Color: Reddish brown, brown, black
Luster: Vitreous to resinous to dull
Transparency: Crystals are translucent to opaque
Crystal System: Monoclinic; 2/m
Crystal Habits: Prismatic to tabular, flattened diamond
shaped cross section. 60 and 90 degree penetration twins
are common (fairy cross)
Cleavage: Poor in one direction.
Fracture: Uneven to conchoidal.
Hardness: 7-7.5
Specific Gravity: 3.7-3.8
Streak: White.
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http://mineral.galleries.com/minerals/silicate/stauroli/stauroli.htm
Phyllosilicates
Micas
Muscovite
„ Micas
ƒ Biotite
ƒ Muscovite
ƒ Others (Lepidolite, etc.)
„ Chlorite
„ Serpentine
Biotite
Lepidolite
„ Talc
„ Clay
minerals
ƒ Kaolinite
Muscovite KAl2(AlSi3O10)(F,OH)2
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Color: White, silver, yellow, green and brown.
Luster: Vitreous to pearly.
Transparency: Crystals are transparent to translucent.
Crystal System: Monoclinic; 2/m
Crystal Habits: include tabular crystals with a prominant
pinacoid termination. Muscovites four prism faces form diamond
shaped "books" and if modified by another pinacoid they form
pseudo-hexagonal crystal "books". The sides of the crystal often
tend to taper. Also as lamellar rock forming masses and small
flakes in detrital material. Twinned crystals can form flat five
pointed stars.
Cleavage: Perfect in one direction producing thin sheets or
flakes.
Fracture: Not readily observed due to cleavage but is uneven.
Hardness: 2 - 2.5.
Specific Gravity: Approximately 2.8 (average)
Streak: White.
http://mineral.galleries.com/minerals/silicate/muscovit/muscovit.htm
Biotite
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K(Fe,Mg)3AlSi3O10(F,OH)2
Color: Black to brown and yellow with weathering.
Luster: Vitreous to pearly.
Transparency: Crystals are transparent to translucent.
Crystal System: Monoclinic; 2/m
Crystal Habits: Tabular to prismatic crystals with a prominant
pinacoid termination. Biotite's four prism faces and two pinacoid
faces form pseudo-hexagonal crystal "books". The sides of the
crystal often tend to taper and can have a "hard candy that has
been sucked on, look". Also as lamellar or granular rock forming
masses providing the luster for most schists and gneiss.
Cleavage: Perfect in one direction producing thin sheets or
flakes.
Fracture: Not readily observed due to cleavage but is uneven.
Hardness: 2.5.
Specific Gravity: Approximately 2.9 - 3.4+ (slightly above
average)
Streak: White.
http://mineral.galleries.com/minerals/silicate/biotite/biotite.htm
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Chlorite, Serpentine and Talc
Chlorite
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Fibrous Serpentine
(Chrysotile Asbestos)
Chlorite
Talc
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(Fe,Mg,Al)6(Si,Al)4O10(OH)8
Color: Usually green but can also be white, yellow, red, lavender and
black.
Luster: Vitreous, dull or pearly.
Transparency: Crystals are translucent transparent.
Crystal System: Monoclinic; 2/m.
Crystal Habits: Rarely in large individual barrel or tabular crystals
with an hexagonal outline. Usually found as alteration products of
iron-magnesium minerals and as inclusions in other minerals.
Aggregates can be scaly, compact, platy and as crusts.
Cleavage: Perfect in one direction, basal; not seen in massive
specimens.
Fracture: Lamellar.
Hardness: 2 - 3
Specific Gravity: Variable from 2.6 - 3.4 (average to slightly above
average)
Streak: Pale green to gray or brown.
http://mineral.galleries.com/minerals/silicate/chlorite/chlorite.htm
Talc Mg3Si4O10(OH)2
Serpentine (Mg,Fe)3Si2O5(OH)4
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Color: Olive green, yellow or golden, brown, or black.
Luster: Greasy, waxy or silky.
Transparency: Crystals are translucent and masses are opaque.
Crystal System: Variable
Crystal Habits: Never in large individual crystals, usually
compact masses or fibrous. Veins of fibrous serpentine can be
found inside of massive serpentine or other rocks.
Cleavage: Varieties of chrysotile have none, in lizardite and
antigorite it is good in one direction.
Fracture: Conchoidal in antigorite and lizardite and splintery in
the chrysotiles.
Hardness: 3 - 4.5 (harder than fingernail)
Specific Gravity: 2.2 - 2.6
Streak: White
http://mineral.galleries.com/minerals/silicate/serpenti/serpenti.htm
Kaolinite Al2Si2O5(OH)4
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Color: Usually white, colorless, greenish or yellow.
Luster: Earthy.
Transparency: Crystals are translucent.
Crystal System: Triclinic; 1.
Crystal Habits: Include foliated and earthy masses.
Crystals of any size are quite rare, usually microscopic.
Cleavage: Perfect in one direction, basal.
Fracture: Earthy.
Hardness: 1.5 - 2 (can leave marks on paper).
Specific Gravity: 2.6 (average).
Streak: White.
http://mineral.galleries.com/minerals/silicate/kaolinit/kaolinit.htm
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Color: Green, gray and white to almost silver.
Luster: Dull to pearly or greasy.
Transparency: Crystals are translucent and masses are opaque.
Crystal System: Monoclinic; 2/m.
Crystal Habits: Never in large individual crystals, but if found
are flattened tabular crystals with a hexagonal cross-section,
usually talc is found in compact or lamellar masses. Forms
pseudomorphs (false shape) of other crystals such as quartz,
pyroxenes, olivine and amphiboles.
Cleavage: Perfect in one direction, basal.
Fracture: Uneven to lamellar.
Hardness: 1 (can leave mark on paper)
Specific Gravity: 2.7 - 2.8 (average)
Streak: White.
http://mineral.galleries.com/minerals/silicate/talc/talc.htm
Kaolinite Al2Si2O5(OH)4
S.E.M. image 1600X
http://mineral.galleries.com/minerals/silicate/kaolinit/kaolinit.htm
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Garnet group
Almandine
nite)
(var. Mela
Andradite
„A
large number of minerals
„ Found in metamorphic rocks
Almandine Fe3Al2(SiO4)3
Andradite Ca3Fe2(SiO4)3
Grossularite Ca3Al2(SiO4)3
Spessartine Mn3Al2(SiO4)3
Uvarovite Ca3Cr2(SiO4)3
Garnet group
„ Easily
identified dodecahedral crystals
„ Hardness – 6.5 to 7 (about the same as
Quartz)
Grossularite
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Color: Typically red to brown, sometimes with a tinge of purple and
sometimes a deep enough red to appear black.
Luster: Vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System: Isometric; 4/m bar 3 2/m
Crystal Habits: Typically a rhombic dodecahedron. Also seen is the
24 sided trapezohedron. Combinations of these forms are common
and sometimes the rare faces of the hexoctahedron, a 48 sided
crystal habit that rarely is seen by itself, can also combine with these
other forms making very attractive, complex and multifaceted
crystals. Massive occurrences are also common. Crystals typically
embedded and isolated, from other alamadine crystals, in
metamorphic rocks.
Cleavage: Absent.
Fracture: Conchoidal.
Hardness: 6.5 - 7.5
Specific Gravity: Approximately 4.3 (above average for translucent
minerals and the highest density of all garnets)
http://mineral.galleries.com/minerals/silicate/almandin/almandin.htm
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Color: Colorless, yellow, orange, green, red, grey and black.
Luster: Vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System: Isometric; 4/m bar 3 2/m
Crystal Habits: Typically rhombic dodecahedrons. Also seen is the
24 sided trapezohedron. Combinations of these forms are common
and sometimes the rare faces of the hexoctahedron, a 48 sided
crystal habit that rarely is seen by itself, can also combine with these
other forms making very attractive, complex and multifaceted
crystals. Massive and granular occurrences are also seen. Commonly
forms crusts that show many rhombic faces.
Cleavage: Absent.
Fracture: Conchoidal.
Hardness: 6.5 - 7
Specific Gravity: Approximately 3.5+ (above average for
translucent minerals).
Streak: White.
http://mineral.galleries.com/minerals/silicate/grossula/grossula.htm
Epidote group
„A
large number of minerals
range of compositions
„ Found in metamorphic rocks
„ Structurally complex
te
Uvarovi
Grossularite Ca3Al2(SiO4)3
Almandine Fe3Al2(SiO4)3
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var. Tsav
orite
Epidote group
Allanite
Epidote
„ Large
Zoisite
Allanite (Ca,Ce,Y,La,Th,Na,K )2(Al, Fe, Be, Mn,
Mg)3(SiO4)3(OH)
Epidote (sensu stricto) Ca2(Al, Fe)3(SiO4)3(OH)
Zoisite and Clinozoisite Ca2Al3(SiO4)3(OH)
http://mineral.galleries.com/minerals/silicate/epidote.htm
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Epidote Ca2(Al,Fe)3(SiO4)3(OH)
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Color: “Pistachio" green to yellowish or brownish green, also
brown to black.
Luster: Vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System: Monoclinic; 2/m
Crystal Habits: Include long, somewhat prismatic or tabular
crystals with a typically dominant pinacoid that the crystal is often
flattened against. The terminations are wedge shaped or tapered
pyramids. Many clusters show grooved slender crystals or acicular
sprays. Also massive, fibrous or granular.
Cleavage: Good in one direction lengthwise.
Fracture: Uneven to conchoidal.
Hardness: 6-7
Specific Gravity: 3.3-3.5
Streak: White to gray
http://mineral.galleries.com/minerals/silicate/epidote/epidote.htm
Clinozoisite
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Color: Gray, apple green, brown, blue, or rose red.
Luster: Pearly to vitreous
Transparency: Crystals are transparent to translucent.
Crystal System: Monoclinic; 2/m
Crystal Habits: Striated, prismatic crystals. Also columnar
forms.
Cleavage: Perfect in one direction lengthwise.
Fracture: Even
Hardness: 6.5
Specific Gravity: 3.3-3.5
Streak: White
http://www.webmineral.com/data/Zoisite.shtml
Tourmaline group
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Easily confused with pyroxene and amphibole.
Triangular, rounded prisms with striations along length
Contains Boron (B)
“Garbage can minerals”, large ranges of composition.
Dravite
Elbaite
Schorl
Uvite
Ca2Al3(SiO4)3(OH)
Tourmaline group
Dravite
Schorl
NaMg3(Al,Fe)6Si6O18(BO3)3(OH)4
Na(Li,Al)3Al6Si6O18(BO3)3 (OH)4
NaFe3(Al,Fe)6Si6O18(BO3)3(OH)4
Ca(Mg,Fe)3Al5MgSi6O18(BO3)3(OH)3
Uvite
Elbaite
http://mineral.galleries.com/minerals/silicate/tourmali.htm
Schorl
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http://mineral.galleries.com/minerals/silicate/tourmali.htm
NaFe3(Al,Fe)6Si6O18(BO3)3(OH)4
Color: Black.
Luster: Vitreous to submetallic.
Transparency: Crystals are opaque.
Crystal System: Trigonal; 3 m.
Crystal Habit: Elongated three sided prisms. The terminations can
be either a simple to complex trigonal pyramid or flat basal face. The
prism faces are usually striated lengthwise. In cross section, all
tourmalines will appear predominantly triangular in shape. Doubly
terminated crystals are hemimorphic meaning that the two ends of
the crystal are not exactly alike. Massive forms can also be found.
Cleavage: Absent although there is basal parting.
Fracture: Uneven to conchoidal.
Hardness: 7 - 7.5 (harder than quartz)
Specific Gravity: 3.2+ (slightly heavier than average)
Streak: White.
Elbaite
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http://mineral.galleries.com/minerals/silicate/schorl/schorl.htm
Na(Li,Al)3Al6Si6O18(BO3)3(OH)4
Color: Extremely variable with the most common colors being red,
pink, green, blue, orange and yellow.
Luster: Vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System: Trigonal; 3 m
Crystal Habit: Typically elongated three, and occasionally six, sided
prisms. The prism faces are striated lengthwise. In cross section, all
tourmalines will appear predominantly triangular in shape with some
crystals showing a hexagon when three secondary prism faces are
nearly as dominant as the three primary prism faces. Acicular and
massive forms can also be found.
Cleavage: Absent, although there is basal parting.
Fracture: Uneven to conchoidal.
Hardness: 7 - 7.5
Specific Gravity: 3.0+ (average)
Streak: White.
http://mineral.galleries.com/minerals/silicate/elbaite/elbaite.htm
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Assorted other minerals
„ Idocrase
Idocrase (Vesuvianite) Ca10(Mg, Fe)2Al4(SiO4)5(Si2O7)2(OH)4
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(Vesuvianite)
Ca10(Mg, Fe)2Al4(SiO4)5(Si2O7)2(OH)4
„ Beryl
Be3Al2(SiO3)6
„ Sphene
CaTiSiO5
„ Topaz
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Al2SiO4(F,OH)3
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Color: Normally green, but also can be brown, yellow, blue and/or
purple.
Luster: Vitreous or greasy to resinous.
Transparency: crystals are transparent to translucent.
Crystal System: tetragonal; 4/m 2/m 2/m
Crystal Habits: Prismatic crystals with an overall square crosssection. There is usually two sets of four sided prisms with one set
being dominant. The termination is usually a four sided pyramid that
can be either steeply or gently sloped. Massive forms are common
and difficult to distinguish from massive garnet.
Cleavage: poor, in one direction lengthwise.
Fracture: Conchoidal to uneven.
Hardness: 6.5 (less than Quartz)
Specific Gravity: 3.3 - 3.5
Streak: White.
http://mineral.galleries.com/minerals/silicate/vesuvian/vesuvian.htm
Beryl
Idocrase (Vesuvianite) Ca10(Mg, Fe)2Al4(SiO4)5(Si2O7)2(OH)4
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http://mineral.galleries.com/minerals/silicate/vesuvian/vesuvian.htm
Be3Al2(SiO3)6
Color: Varied and includes emerald green, blue to blue-green,
yellow, greenish-gold, red, colorless and pink.
Luster: Vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System: Hexagonal; 6/m 2/m 2/m
Crystal Habits: Hexagonal prisms with pincoid terminations.
The terminations are often modified by many different
pyramidal faces which can sometimes produce a rounded
termination in the rough shape of a used pencil eraser.
Cleavage: Imperfect in one direction (basal).
Fracture: Conchoidal.
Hardness: 7.5 – 8 (harder than quartz, softer than corundum)
Specific Gravity: Approximately 2.6 - 2.9 (average)
Streak: White.
http://mineral.galleries.com/minerals/silicate/beryl/beryl.htm
Sphene CaTiSiO5
Aquamarine
(b
lue)
Beryl Be3Al2(SiO3)6
Heliodor (yellow
E me
rald
e
(gre
n)
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Morganite (pink)
Goshenite (colorless)
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Color: Green, yellow, white, brown or black.
Luster: Adamantine.
Transparency: Crystals are transparent to translucent.
Crystal System: Monoclinic; 2/m
Crystal Habits: Elongated wedges that form tabular or platy
crystals. Some crystals are not so elongated and can have a
trigonal appearance similar to a flattened rhombohedron.
Twinning is common and produces a twin that is shaped like a
deflated, caved-in football, only with flatter surfaces.
Cleavage: Indistinct in two directions
Fracture: Conchoidal
Hardness: 5 - 5.5
Specific Gravity: 3.3 - 3.6
Streak: White.
http://mineral.galleries.com/minerals/silicate/sphene/sphene.htm
6
Sphene CaTiSiO5
Topaz Al2SiO4(F,OH)3
Color: Clear, yellow, orange, red, blue and green.
„ Luster: Adamantine to vitreous.
„ Transparency: Crystals are transparent to translucent.
„ Crystal System: Orthorhombic; 2/m 2/m 2/m
„ Crystal Habits: Prismatic crystal with usually two different
prisms that produce a rounded or sharp diamond-shaped
cross-section. Granular and massive varieties are also found.
„ Cleavage: Perfect in one direction, basal.
„ Fracture: Conchoidal.
„ Hardness: is 8 (harder than Quartz, softer than
Corundum).
„ Specific Gravity: Approximately 3.4 - 3.5+ (above
average)
„ Streak: white (scratches scratch plate).
http://mineral.galleries.com/minerals/silicate/sphene/sphene.htm
http://mineral.galleries.com/minerals/silicate/topaz/topaz.htm
Topaz Al2SiO4(F,OH)3
http://mineral.galleries.com/minerals/silicate/topaz/topaz.htm
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