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Inorganics

Id Identification Type Name Description Distinguishing Features Tags
107 Mineral Albite Clear to pale yellow. Nonpleochroic. Low birefringence. Euhedral laths possible in volcanic settings, generally subrounded/subangular in shape. High relief. Can be distinguished from quartz by its 90 degree cleavage. Polysynthetic (albitic, simple) twinning is diagnostic. Sodium endmember of plagioclase solid solution series.

See also feldspar.

"Elongate prisms in multiple domains" -Smoot
polysynthetic-twinning feldspar
silicate
plagioclase
21 Mineral Amphibole Transparent colorless to green, brown, red, yellow, depending on mineralogy within the amphibole group. Strongly pleochroic. Moderate birefringence may be masked by color. Anhedral to euhedral prismatic grains. High relief. Hornblende-series minerals the most common detrital amphiboles. Pleochroic
Subhedral
Prismatic
ferromagnesian
high-relief
green
silicate
transparent
green
62 Mineral Apatite Usually transparent colorless. Nonpleochroic. Weak birefringence (white-gray). Prismatic, six-sided crystals may be euhedral or subhedral. Moderate relief. May occur as either detrital grains (derived from felsic igneous rocks) or authigenic/diagenetic crystals in phosphate-rich environments. Prismatic
Moderate-relief
Colorless
Transparent
low-birefringence
anisotropic
euhedral
phosphate
heavy-mineral
37 Mineral Aragonite Transparent colorless. Nonpleochroic. Extreme birefringence. Distinguished by small (~10 um) acicular (needle-like) or rice-like grain morphology. Moderate relief, varying by direction. Twinning may be common.

Organisms such as pteropods, most mollusks, and some corals produce biogenic aragonite.
Rice-shape
Acicular
Elongate
High-birefringence
Carbonate
salt
transparent
colorless
180 Contaminant Backer rod contaminant
175 Lithofacies Banded carbonate mud
22 Mineral Biotite Occurs as flakes larger than surrounding material, green to brown transparent, may be pleochroic. Low to moderate relief. Cleavage planes frequently visible as platy layers. Classic bird's eye extinction (mottled, pebbly texture) not always present in smear slide. Very low apparent birefringence (pseudo-isotropy) because flakes settle with {001} in the plane of the slide. However, by tilting the slide very slightly (e.g., by slipping another slide under the slide) one can evaluate the true birefringence (thanks to Frank Brown, U. Utah, for the tip). Biotite has strong birefringence; chlorite, which may form as an alteration product or a metamorphic mineral, can look similar to biotite in plane light but has weak birefringence. Flaky
Pseudo-isotropic
Pleochroic
bird's-eye-extinction
brown
green
layers
ragged
silicate
mica
transparent
117 Contaminant Bubble Transparent colorless with heavy black outline. Nonpleochroic, isotropic. Bubbles in optical cement are typically circular but can be any shape when filling voids in biological remains. Very high relief, and may be out of plane of focus of other materials due to larger size. May occur in any slide. Can be partially avoided by keeping bottle of mounting medium upside down when not in use, and mounting several slides at a time so that bubbles are only present in first one or two. High-relief
spherical
circular
dark
high-relief
transparent
contaminant
115 Lithofacies Calcareous silt
38 Mineral Calcite Transparent colorless to pale greenish. High birefringence. Rhombic or ellipsoidal euhedra, corroded grains, micritic masses most common; more rarely twins, bow-ties, dendrites, sprays. Medium relief. Occurs as inorganic precipitate in lakes, in surface water and diagenetically (including as a replacement); also irregular detrital grains and rock fragments.

Organisms with calcite skeletal components include ostracodes, some molluscs, foraminifera, coccoliths, calcareous nannoplankton, Phacotus, charophytes, peloids, microbialites.
High-birefringence
Transparent
carbonate
Colorless
Rhombic
euhedral
salt
23 Mineral Chlorite Colorless to yellow or green, transparent, generally pleochroic. Low to moderate relief. Cleavage planes frequently visible as platy layers. Very low apparent birefringence (pseudo-isotropy) because flakes settle with {001} in the plane of the slide. However, by tilting the slide very slightly (e.g., by slipping another slide under the slide) one can evaluate the true birefringence (thanks to Frank Brown, U. Utah, for the tip). Chlorite has weak birefringence and can have anomalous (purplish or brown) interference colors due to its varying chemistry. Occurs as flakes larger than surrounding material when primary, can be fibrous or granular when replacing other minerals. Flaky
Pseudo-isotropic
yellow
green
layers
ragged
silicate
mica
transparent
low-birefringence
144 Contaminant Cigarette Ash contaminant
16 Mineral Clay
170 Lithofacies Clay turbidite cap
51 Mineral Clinoptilolite Associated with devitrified volcanic glass.
29 Mineral Clinopyroxene Transparent colorless to green or brown. May be pleochroic from yellow to green, depending on mineralogy. Moderate birefringence. Appear as stubby prisms and subhedral to anhedral crystals. Near-90 degree perfect cleavage. Moderately high relief. Subhedral
near-90-degree-perfect-cleavage
ferromagnesian
silicate
transparent
green
brown
pleochroic
moderately-high-relief
8 Mineral Cosmic Spherule
169 Lithofacies Diatom ooze
114 Lithofacies Diatomaceous carbonate mud
39 Mineral Dolomite Transparent colorless. Nonpleochroic. Extremely high birefringence. Equant cleavage rhombs, usually with sharp edges. High relief. Usually detrital but may be authigenic in some rare environments. Usually small (fine silt to clay) grains. Higher relief than calcite, and rhombs generally more equant than calcite, but can be difficult to conclusively distinguish from calcite. Rhombic
High-birefringence
carbonate
cleavage
high-relief
equant
transparent
colorless
salt
104 Mineral Fecal pellet
68 Mineral Feldspar Transparent colorless to cloudy. Nonpleochroic. Low order birefringence. Tabular to prismatic. Relief varies by composition.

"Feldspar" includes several minerals or groups of minerals with solid solutions. According to Rothwell (1989, p.77) the distinguishing features of feldspars are "Subhedral prismatic to tabular form, turbidity due to incipient alteration, distinctive twinning (seen in cross-polars) ... Low birefringence."

Alkali feldspars tend to display simple Carlsbad twinning, though Carlsbad twinning can be found in all feldspars (Rothwell, 1989, p.74). Grid (cross-hatched polysynthetic) twinning in two directions is a diagnostic characteristic of microcline, and lamellar (multiple) twinning occurs mainly in plagioclase (Rothwell, 1989, p.74). The width of lamellae in plagioclase relates to composition, with more narrow lamellae in oligoclase and wider lamellae in albite and anorthite (Rothwell, 1989, p.75).

More quantitative distinction between plagioclase feldspar minerals of individual mineral grains can be achieved using the Michel-Levy method, which is based on the maximum extinction angles of twin lamellae (Rothwell, 1989, p.71-73). Refer to Rothwell (1989) p.71-73 for a step-by-step description of the Michel-Levy method.

Some identifiable feldspars are listed separately in TMI: albite, microcline, and orthoclase.
good-cleavage
low-birefringence
feldspar
silicate
twinned
transparent
translucent
124 Contaminant Fiber contaminant
145 Contaminant Floral Foam contaminant
33 Mineral Garnet Transparent colorless to rose or amber. Isotropic. Very high relief. Equant rounded grains are most common, but may also occur as etched and irregular grains. Cleavage absent. Occurs as smaller grains than other minerals in slide because of garnet's higher density. Isotropic
Heavy-mineral
pink
brown
silicate
174 Lithofacies Glacial varves
15 Mineral Glauconite Blue green to olive green. Often occurs as sand-sized, rounded pellets. Secondary mineral. green
159 Mineral Greigite
46 Mineral Gypsum Transparent colorless. Nonpleochroic. Low birefringence (about the same as quartz). May occur as thin plates (folia), tabular euhedra, or acicular needles. Low relief. Detrital or authigenic. Frequently associated with pyrite when authigenic. May be twinned. Caution: common precipitate from pore waters of cores as they age in storage. Also, heating slide may cause polysynthetic twinning. Low-relief
Low-birefringence
Tabular
Acicular
143 Contaminant Hair contaminant
135 Mineral Inclusion
10 Mineral Industrial Spherule
14 Mineral Iron (Hydr)oxides, Non-opaque (Hematite/Limonite) Non-opaque iron oxides, hydroxides, and oxyhydroxides including hematite (which may also occur as opaque grains) and limonite (actually a mixture of minerals including goethite). Red to brown; limonite yellower. High relief. May occur as granular aggregates, scales, either translucent or transparent. May be isotropic or show low-order birefringence.

Hematite is red to brown, transparent to opaque. Red-brown in reflected light. Hematite has high birefringence, but may not be observable due to deep color of grains. Some hematite grains may be noncrystalline and thus isotropic. Irregularly shaped flakes and earthy or somewhat fibrous particles. High relief. Hematite occurs as detrital or authigenic/diagenetic grains.
Translucent
Transparent
Granular
red
brown
yellow
6 Mineral Iron Oxides, Opaque (e.g., Magnetite) heavy-mineral
146 Contaminant Kimwipe contaminant
147 Contaminant Lab Dust contaminant
168 Lithofacies Laminated sulfidic silt
132 Mineral Lithic fragment Wide variety of forms and optical properties. A very small rock made up of one or more minerals. Can be identified by the presence of grain boundaries within a particle. grain-boundaries
102 Mineral Magadiite Rare evaporite mineral common to Lake Magadi, Kenya. silicate
evaporite
transparent
colorless
55 Mineral Microcline Transparent colorless. Nonpleochroic. Low order birefringence colors. Distinctive twinning pattern from the intersection of pericline and albitic twins ("tartan plaid" or "cross-hatched") in cross-polarized light is virtually diagnostic of microcline. Tabular and cleavage fragments. Moderate relief.

See also feldspar.
tartan-twinned
low-birefringence
silicate
plaid
tartan
cross-hatch
twinned
feldspar
cleavage
transparent
colorless
7 Mineral Micronodule
148 Contaminant Mold contaminant
48 Mineral Muscovite Transparent, colorless. Strong second-order birefringence. Shredded or stringy texture common. Low relief. Usually does not look similar to biotite. Shredded
Stringy
Colorless
High-birefringence
ragged
transparent
mica
silicate
40 Mineral Olivine Transparent colorless to pale gray-green. Nonpleochroic. Vivid birefringence colors. Frequently occurs as subangular anhedral grains. Conchoidal fracture. Moderately high relief. Associated with calcic plagioclase and pyroxene. Conchoidal-fracture
Moderately-high-relief
Anhedral
silicate
ferromagnesian
transparent
colorless
gray
103 Mineral Opal
116 Lithofacies Organic-rich carbonate mud with pyrite
163 Lithofacies Organic-rich Diatom Ooze Dominantly composed of diatoms and algal organic matter. circular
transparent
colorless
rice-shape
brown
amorphous
53 Mineral Orthoclase Colorless to pale yellow, nonpleochroic, low birefringence, commonly elongate when euhedral, moderate to high relief, contact twinning is virtually diagnostic (only one twin plane in a single crystal).

See also feldspar.
no-lamellar-twinning
contact-twinning
feldspar
silicate
28 Mineral Orthopyroxene Transparent colorless to green or brown. May be pleochroic from pale red to greenish (hypersthene). Low birefringence. Appear as stubby prisms and subhedral to anhedral crystals. Near-90 degree perfect cleavage. Moderately high relief. Subhedral Ferromagnesian
pleochroic
silicate
transparent
brown
green
good-cleavage
moderately-high-relief
13 Mineral Palagonite
164 Lithofacies Peat
52 Mineral Phillipsite zeolite
111 Mineral Pirssonite
54 Mineral Plagioclase Plagioclase is a term for feldspars in the Na-Ca solid solution series. Without twinning patterns, there is no way to tell a difference between Na-Ca feldspars and K-feldspars (microcline and orthoclase). lamellar-twinning
low-birefringence
silicate
149 Contaminant Polycarb Large Fragment contaminant
150 Contaminant Polycarb Small Fragment contaminant
5 Mineral Pyrite Opaque (black). Yellow in reflected light. Pleochroism and birefringence not applicable. Euhedral, framboidal, space-filling shapes. May coat or replace organic matter. Occurs in organic-rich or reduced sediments. Common in lacustrine, wetland, estuarine, and marine environments. Opaque
euhedral
Cubic
Octahedral
Framboidal
sulfide
138 Mineral Pyroxene silicate
47 Mineral Quartz Transparent colorless; equant grains; cleavage absent. Grains larger than ~30um show higher order birefringence colors (dark orange, pink), while smaller grains appear white or gray in cross-polarized light. May appear pitted, or show opaque or reddish coatings visible in plane polarized or reflected light. May be well-rounded where aeolian or fluvial transport contributes. Common mineral in detrital sediments and rock fragments. Low-birefringence
Equant
silicate
Transparent
Colorless
Low-relief
60 Mineral Rhodochrosite Greenish-brown in plane light. Strongly pleochroic. High birefringence. Ellipsoidal; may be difficult to distinguish in smear slide from siderite or dolomite. Forms in environments with reduced Mn. Occurs in lakes and estuaries, but uncommon; rare to absent in marine settings. Brown-green
High-birefringence
120 Mineral Rutile Transparent gray-green. Nonpleochroic. Strong second-order birefringence with vivid colors. High relief.

Usually detrital, but in rare cases may form diagenetically (M. Talbot, pers. comm). May appear as multiple contact twins.
high-relief
transparent
twinned
heavy-mineral
42 Mineral Serpentine minerals
97 Mineral Siderite Transparent pale green to orange-brown. Nonpleochroic. High-order birefringence. Moderate relief.

Form is somewhat diverse, due to varying means of formation. Common forms are elongate laths with squared off ends and parallel sides (easily distinguished from rice grain shaped aragonite and more rhombic calcite), twinned "bowtie" shapes of multiple laths, or granular rounded euhedra.

Requiring reduced iron, siderite, FeCO3, usually forms deep in the water column, when anoxic bottom waters mix with carbonate-rich surface waters, or diagenetically. Massive amounts of siderite may be precipitated rapidly, and may or may not be cemented with siderite or other phases.
carbonate
green
brown
151 Contaminant Slide Glass Slide manufacturing and handling can sometimes produce fine shards that mimic volcanic glass. Pre-cleaning of new slides prior to smear slide preparation can help minimize encounters with this confusing artifact. isotropic conchoidal-fracture contaminant
73 Mineral Sulfur
61 Lithofacies Tephra Tephra, or volcanic ash, is a mixture of volcanic glass and crystalline grains derived from the same volcanic source. A tephra unit in a core may be predominantly crystalline and coarse-grained at the base, grading upwards to finer, more glassy grains. See volcanic glass for a detailed description and identification; crystalline components can be identified based on their optical mineralogical characteristics. isotropic volcanic-glass
172 Lithofacies Tephra - Glacier Peak G
179 Lithofacies Tephra - mafic
177 Lithofacies Tephra - Mount Saint Helens
173 Lithofacies Tephra - Mt. St. Helens J
176 Lithofacies Tephra- Mazama
118 Contaminant Toothpick Small fibers from wooden toothpicks used to disperse sediment on smear slides can be confused with muscovite. Transparent, colorless. Strong second-order birefringence. Shredded or stringy texture common. Low relief. Cellular structure may be visible and can be used to distinguish toothpick from muscovite Shredded
Stringy
Colorless
High-birefringence
Cellular-structure
contaminant
71 Mineral Tourmaline Transparent, variety of colors or colorless. Pleochroic (variable with composition). Moderate birefringence giving vivid colors. Elongate prismatic crystals to rounded grains. Moderate to high relief. Straight extinction. Often has inclusions. Prismatic
Pleochroic
Heavy-mineral
silicate
moderate-birefringence
elongate
high-relief
112 Mineral Trona
171 Lithofacies Turbidite
165 Lithofacies Turbidite sequence
59 Mineral Vivianite Blue in both plane and cross-polarized light. May occur in diagenetic sprays, euhedra, nodules, and coatings. Low birefringence. In core face, chalky white when reduced; bright blue when oxidized. Associated with organic matter, bones, teeth, seeds, and other environments with available phosphate and reduced iron. Commonly found in lacustrine and estuarine sediments. Not common in marine sediments. Blue
Pleochroic
phosphate
transparent
diagenetic
ferrous
27 Mineral Volcanic Glass Transparent colorless to pale gray, green, or brown. Nonpleochroic. Isotropy is diagnostic feature, although devitrification may cause low-order birefringence at edges of grains. Moderate relief. May have bubble or pipe vesicles, stretching textures, cuspate to lunate bubble wall shards with sharp edges. May be disseminated throughout other sediment or occur in pure layers. Tephra may also contain crystalline grains from the same eruption or reworked material. Isotropic
Vesicular
bubbles
shards
sharp
ash
9 Mineral Volcanic Spherule
49 Mineral Zeolite
70 Mineral Zircon Transparent colorless to pale pink. Nonpleochroic. High order birefringence. Elongate euhedra, often with inclusions aligned along the long axis of the grain. Very high relief. Straight extinction. Heavy-mineral
High-relief
silicate
inclusions
nonpleochroic
high-birefringence
transparent
152 Contaminant Zorbitrol Zorbitrol is a hydrophilic sodium acrylate polymer sometimes used to physically stabilize the surface of sediment cores. contaminant