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.