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Inorganics

Id Identification Type Name Description Distinguishing Features Tags
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