| Id | Identification Type | Name | Description | Distinguishing Features | Tags |
|---|---|---|---|---|---|
| 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 conchoidally fractured volcanic glass (typically dominant) in variable proportions with crystalline volcanic constituents. Glass may be altered to any of a suite of secondary minerals, typically of low and variable birefringence. |
volcanic-glass isotropic conchoidal vesicular |
|
| 172 | Lithofacies | Tephra - Glacier Peak G | Lithofacies defined as the directly deposited ejecta from the 'Series G' Plinian eruption of Glacier Peak, Washington state, ca. 13500 cal. yr BP.
Distinguished indisputably by elemental chemistry. Identification is frequently inferred by bracketing ages, geographic distribution, and general appearance. |
volcanic-glass isotropic conchoidal vesicular Cascades |
|
| 179 | Lithofacies | Tephra - mafic | Lithofacies defined as the directly deposited ejecta of mafic (typically basaltic) volcanic eruptions. | ||
| 177 | Lithofacies | Tephra - Mount Saint Helens Y | Lithofacies defined as the directly deposited ejecta from the 'Series Y' eruption of Mt. Saint Helens, Washinton state, ca. 3750 cal. yr BP.
Distinguished indisputably by elemental chemistry. Identification is frequently inferred by bracketing ages, geographic distribution, and general appearance. |
volcanic-glass isotropic conchoidal vesicular Cascades |
|
| 173 | Lithofacies | Tephra - Mt. St. Helens J | Lithofacies defined as the directly deposited ejecta from the 'Series J' eruption of Mt. Saint Helens, Washinton state, ca. 12000(?) cal. yr BP.
Distinguished indisputably by elemental chemistry. Identification is frequently inferred by bracketing ages, geographic distribution, and general appearance. |
volcanic-glass isotropic conchoidal vesicular Cascades |
|
| 176 | Lithofacies | Tephra- Mazama | Lithofacies defined as the directly deposited ejecta from the cataclysmic Plinian eruption of Mt. Mazama, Oregon, ca. 7630 cal. yr BP.
Distinguished indisputably by elemental chemistry. Identification is frequently inferred by bracketing ages, geographic distribution, and general appearance. |
volcanic-glass isotropic conchoidal vesicular Cascades Holocene |
|
| 185 | Mineral | Titanite | Very high-relief Ti-Ca silicate mineral with prominent acutely angled twinning.
High birefringence, but high optical relief may obscure interference colors in small detrital grains. May occur as part of winnowed heavy-mineral assemblages in littoral sediments or as part of heavy-mineral lag deposits on surfaces of aeolian deflation. |
high-birefringence | |
| 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 | Colorless (sometimes cloudy), prismatic or acicular, moderately high relief and high birefringence; may be striated parallel to long dimension. Trona is an evaporite mineral formed in hypersaline lakes or as an efflorescent precipitate on sediment surfaces. Highly soluble in water, and will dissolve and re-precipitate during smear slide manufacturing if water is used; slides should be made using ethanol if the presence of evaporate minerals is suspected. | high-birefringence
striated monoclinic-habit water-soluble |
|
| 165 | Lithofacies | Turbidite sequence | Lithofacies comprising one or more graded beds, interpreted as the product of gravity-driven mass transport and density separation of sediment constituents.
Sharp, sometimes erosional basal contact; normal (fining-upward) size grading; may have distinctive light-colored uppermost layer of fine silt or clay-sized material; may have relative concentration of heavy minerals at deposit base. |
graded density gravity-deposit Bouma-sequence |
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