Clastic sandstone with more than 10 percent matrix of indeterminate detrital or diagenetic
nature. Matrix is mud size silicate minerals (clay, feldspar, quartz, rock fragments,
and alteration products).
Distinction from mudstone is based on inference that less that 50 percent of the mud
size fraction (matrix) is original mud size detrital particles. May also grade into
diamictite or conglomerate based on size distribution of discernible particles. If
more than 50 percent of rock is detrital particles of intrabasinal orgin and carbonate
composition, categorize as carbonate wackestone. Term is typically applied to diagenetically
altered volcanic-lithic clastic rocks in which the definition of the original clasts
has been obscured. Suggested boundaries between wacke and arenite range from 5 to
15 percent matrix. See Dickinson (1970) for discussion of interpretation of undiscernible
matrix in diagenetically altered lithic clastic rocks. Dickinson, W.R., 1970, Interpreting
detrital modes of graywacke and arkose: Journal of Sedimentary Petrology, v. 40, p.
Pettijohn, Potter, Siever, 1972, Sand and Sandstone: New York, Springer Verlag, 681
Rock consists of more than 50 percent particles of indeterminate pyroclastic or epiclastic
origin and less than 75 percent particles of clearly pyroclastic origin. commonly
the rock is laminated or exhibits size grading. (based on LeMaitre et al. 2002; Murawski
and Meyer 1998).
volcaniclastic sedimentary rock
In practice, it is likely that any rock for which there is suspicion that it may consist
of redeposited pyroclastic material, usually based on sedimentary structures, irrespective
of the presence or percentage of clearly epiclastic particles, would be called a tuffite.
50 percent cutoff with epiclastic rock is in contrast with LeMaitre et al., but is
used for consistentency with other sedimentary rock categories following the pattern
that the rock name reflects the predominant constituent.
Biotically or abiotically precipitated calcium carbonate, from spring-fed, heated,
or ambient-temperature water. May be white and spongy, various shades of orange, tan
or gray, and ranges to dense, banded or laminated rock. Macrophytes, bryophytes, algae,
cyanobacteria and other organisms often colonize the surface of travertine and may
be preserved, to produce the porous varieties.
Neuendorf et al. 2005; http://en.wikipedia.org/wiki/Travertine; Chafetz, H.S., and
Folk, R.L., 1984, Travertine: Depositional morphology an dthe bacterially constructed
constituents: J. Sed. Petrology, v. 126, p.57-74.
Fine grained igneous rock than contains less than 90 percent mafic minerals, less
than 10 percent feldspathoid mineral and less than 20 percent quartz in the QAPF fraction
and has a plagioclase to total feldspar ratio less than 0.65. Mafic minerals typically
include amphibole or mica; typically porphyritic. Includes rocks defined modally in
QAPF fields 6, 7 and 8 (with subdivisions) or chemically in TAS Field T as trachyte
LeMaitre et al. (2002) used 'trachyte' to refer to QAPF fields 7, 7', and 7* in the
text (p. 30) as well as to the more restrictive category (QAPF field 7 only). The
term Trachytic rock is introduced here to label this more general category of trachyte.
Granitoid consisting of quartz and intermediate plagioclase, usually with biotite
and amphibole. Includes rocks defined modally in QAPF field 5; ratio of plagioclase
to total feldspar is greater than 0.9.
Tholeiitic basalt is defined here to contain 2 pyroxene phases and interstitial quartz
or tridymite or cristobalite in the groundmass. Pyroxene (augite and orthopyroxene
or pigeonite) and calcium-rich plagioclase are common phenocryst minerals. Olivine
may also be a phenocryst, and when present, may have rims of pigeonite. Only in tholeiitic
basalt is olivine in reaction relationship with melt. Interstitial siliceous residue
may be present, and is often glassy. Tholeiitic basalt is relatively poor in sodium.
This category includes most basalts of the ocean floor, most large oceanic islands,
and continental flood basalts such as the Columbia River Plateau.
Definition of tholeiite and alkali basalt here are more proscriptive than those found
in most reference authorities. This is to actually provide some descriptive criteria
to allow assignment of rocks on a hand sample basis to the tholeiite or alkali basalt
categories if detailed petrographic or chemical data are available.
http://en.wikipedia.org/wiki/Basalt; Carmichael, I.S. Turner, F.J., Verhoogen, John,
1974, Igneous petrology: New York, McGraw HIll Book Co., p.42-43.
Fine grained igneous rock than contains less than 90 percent mafic minerals, between
10 and 60 percent feldspathoid mineral in the QAPF fraction and has a plagioclase
to total feldspar ratio greater than 0.5. Includes rocks classified in QAPF field
13 and 14 or chemically in TAS field U1 as basanite or tephrite.
Foiditoid that contains less than 90 percent feldspathoid minerals in the QAPF fraction,
and has a plagioclase to total feldspar ratio that is greater than 0.5, with less
than 10 percent normative olivine
Unconsolidated pyroclastic material in which greater than 75 percent of the fragments
are deposited as a direct result of volcanic processes and the deposit has not been
reworked by epiclastic processes. Includes ash, lapilli tephra, bomb tephra, block
tephra and unconsolidated agglomerate.
Phaneritic crystalline igneous rock with M less than 90, consisting mainly of alkali
feldspar and plagioclase; minor quartz or nepheline may be present, along with pyroxene,
amphibole or biotite. Ratio of plagioclase to total feldspar is less than 0.65, quartz
forms less than 20 percent of QAPF fraction, and feldspathoid minerals form less than
10 percent of QAPF fraction. Includes rocks classified in QAPF fields 6, 7 and 8 and
Altered basic to intermediate composition fine-grained igneous rock in which the feldspar
is partially or completely composed of of albite, typically accompanied by chlorite,
calcite, quartz, epidote, prehnite, and low-tempaerature hydrous crystallization products.
Preservation of eruptive volcanic features is typical.
Fettes and Desmon, 2007; Best, M.G., 1982, Igneous and metamorphic petrology: New
York, W.H. Freeman and company, p. 398; Neuendorf et al. 2005, p. 619.
Metasomatic rock consisting mainly of Ca-, Mg-, Fe-, or Mn-silicate minerals, which
are free from or poor in water. Typically formed at the contact between a silicate
rock or magma and a carbonate rock.
Mudstone that contains detectable silt. (see comments)
Use of 'dectable silt' in the criteria for this category is based on the observation
that in practice, distinction of claystone from 'siltstone' is typically based on
a qualitative assessment of 'grittiness' (e.g. rubbing with fingers, or chewing);
the property that these tests can determine is the presence or absence of silty particles
in the material. Quantitative grain size analysis in the the clay/silt fraction of
a lithified sediment is difficult at best, and of questionable significance because
diagensis has altered the size and mineralogy of original sedimentary particles.