From Wikipedia, the free encyclopedia
Very fine-grained volcanic rock that sometimes contains larger crystals
Felsite covered with
dendritic
pyrolusite
formations.
Dike
of felsite on
Islay
in Scotland
Felsite
is a very fine-grained
volcanic rock
that may or may not contain larger
crystals
. Felsite is a field term for a light-colored rock that typically requires
petrographic
examination or chemical analysis for more precise definition. Color is generally white through light gray, or red to tan and may include any color except dark gray, green or black (the colors of
trap rock
).
[1]
The mass of the rock consists of a fine-grained
matrix
of
felsic
materials, particularly
quartz
,
sodium
and
potassium feldspar
,
[2]
and may be termed a quartz felsite or quartz porphyry if the quartz phenocrysts are present. This rock is typically of
extrusive
origin, formed by compaction of fine volcanic ash, and may be found in association with
obsidian
and
rhyolite
. In some cases, it is sufficiently fine-grained for use in making
stone tools
. Its fine texture and felsic components allow for good knapped pieces, much like working
chert
, producing
conchoidal fracture
.
Dendritic
manganese oxides such as
pyrolusite
and/or iron oxides such as
limonite
may precipitate along rock crevices, giving some rock chunk surfaces multicolored or arborescent patterned textures.
References
[
edit
]
- ^
Klein, Cornelis and Hurlbut, Cornelius S. (1986),
Manual of Mineralogy,
Wiley, p. 484
ISBN
0-471-80580-7
- ^
McDonnell, S.; Troll, V. R.; Emeleus, C. H.; Meighan, I. G.; Brock, D.; Gould, R. J. (October 2004).
"Intrusive history of the Slieve Gullion ring dyke, Ireland: implications for the internal structure of silicic sub-caldera magma chambers"
.
Mineralogical Magazine
.
68
(5): 725?738.
Bibcode
:
2004MinM...68..725M
.
doi
:
10.1180/0026461046850215
.
ISSN
0026-461X
.
S2CID
140159457
.