( Fr- granit; Ger- Granit; Nor- granitt; Rus- )
A. Granite. Pin with granite pendant (greatest dimension - ~ 3.5 cm ) that is a tumbled piece of granite from Barre, Vermont region. F.S. Dietrich collection. (© photo by Dick Dietrich)
B. Granite from vicinity of St. Cloud, Minnesota (width - 5 cm), that exhibits a typical granitic texture. (© photo by B.J. Skinner)
C. Granodiorite bookend (height - 15 cm) presented to Adolph Knopf by his students upon his retirement as Sterling Professor of Petrology at Yale University. R.V. Dietrich collection. (© photo by Dick Dietrich)
DESCRIPTION: Granite, is defined
by most professional geologists as a phaneritic igneous rock that
consists of 20 or more percent quartz, more alkali feldspar than
plagioclase feldspar, and between 5 and 20 percent varietal minerals
(typically biotite + muscovite + hornblende). A few
geologists, who think that at least some granites are not of igneous
origin, substitute "igneous or igneous-appearing" for igneous
in the just reiterated definition. Properties
of the chief minerals, as they occur in granitic rocks, follow: Quartz -- colorless,
milky white or smoky (gray-tan); H. 7; S.G. 2.65; transparent to
translucent; vitreous luster; conchoidal fracture. Alkali
feldspar (which includes microcline, orthoclase and perthite) --
off-white, light tan, salmon-pink to nearly brick-red; H. 6-6½;
S.G. 2.55-2.63; subtranslucent to opaque; pearly luster; two good
cleavages at or near 90 degrees to each other. Plagioclase
feldspar (which in granitic rocks is typically oligoclase) --
off-white to buff; H. 6-6½; S.G. 2.61-2.64; subtranslucent to
opaque; pearly luster; two cleavages a few degrees off 90 degrees to
each other; polysynthetic twinning -- which is expressed by closely
spaced parallel lines that can be seen when certain cleavage surfaces
are viewed through a simple (e.g., 10x) hand lens -- is
common. As a consequence of the mineral constitutuents, granites
have the following overall properties:
Colors - typically overall gray or salmon pink to nearly brick red
H. (effective hardness) 7
Light transmission - opaque
Luster - ranges from dull to grainy with sporadic parts pearly and vitreous
Breakage - irregular
Miscellany - In the marketplace, the term granite is frequently extended to include virtually all relatively light colored igneous and igneous-appearing rocks that roughly resemble granite, sensu stricto. -- Most of the other rocks that are so-designated in the market are monzonites and granodiorites, but a few are diorites and syenites according to accepted petrographic nomenclature. A well known example of these marketplace "granites" is the Mount Airy Granite of North Carolina, which in professional petrographic literature should be called a leuco-granodiorite. Definitions of the names applied by petrographers to these other "granites" are given in the GLOSSARY and general relationships among these rocks can be seen in books such as "Rocks and Rock Minerals" by Dietrich and Skinner (1979).
Herein, marketplace usage is followed -- i.e., granite is used to include all relatively light colored (overall nearly white, gray, tan, pink and reddish) phaneritic igneous and igneous-appearing rocks that have a typical granularity. All consist largely of one or two feldspars and quartz plus or minus some dark-colored mineral such as biotite (=black mica); H. >6 (= effective hardness); S.G. ~ 2.65. Also, it seems prudent to note that several of these rocks are gneissic.
OTHER NAMES: Granite, granodiorite, etc.
are widely accepted petrographic designations. Several granite (etc.)
masses around the world have been named on the basis of their locations
and are shown on geologic maps and referred to in geological reports by
those binomial names -- e.g., the Barre Granite of central
Vermont, the St. Cloud Granite of eastern Minnesota, and the Clancy
Granodiorite, which was named by Adolph Knopf, to whose memory this
compilation is dedicated, for exposures in Kain quarry on Clancy Creek,
Lewis and Clark County, Montana. Several of the
geographically based names of granites (etc.) are also used in the
In addition, granites (etc.) of certain overall colors or
exhibiting certain relatively distinct appearances have been given
names that relate to those characteristics, and those names are used
along with or
instead of the formal geographically based names. And, a few of
these rocks have been and continue to be used as gemrocks. Two
OCCURRENCES: As relatively large igneous or igneoid masses.
Vermont; St. Cloud, Minnesota.
Origin of the name granite traces
back to the Italian granito,
which is the past participle of granire,
which means to make grainy; Granire, in turn, is from grano (grain) from the Latin grānum, said to have Indo-European
roots. Its use as a rock name dates back to at least the early
Three major uses of rocks widely marketed as granites are for ashlar (for both exterior and interior facings), tombstones and other monuments and sculptures.
In the literature, several rocks other those mentioned under OTHER NAMES have been called granite, usually with some modifying adjective. Among those I have seen so-labeled are rocks included in the GNEISS and AMPHIBOLITE entries in this book and even BASALT (called black granite), none of which is a granite.
So far as the use of granites as decorative stones, the following quotation from the preface to The Marbles and Granites of the World (Grant, 1955) seems noteworthy.
"The author was led [to compile the information published in this book because of his] ... realisation of the artistry of the patterns and colouration of almost all the rocks of the earth. [He believes] ... a humble stone will delight the cultured observer even more than the polychrome of far more brilliant objects. [And, consequently] these Marbles and Granites, then, may be regarded ... as pictures, or at least as colour-schemes designed at the dawn of the world. [So,] they are thus not as incompatible as might be thought with Art, the subject of his previous volumes, but an interesting, and to many perhaps a novel aspect thereof."
especially interesting, remarkably
detailed ancient sculpture is illustrated in the July/August
issue of "Saudi Aramco World" (page 16): It is described
as sculpted by "a royal architect ... , made
diorite about 2090 BC, ... [and] found at Girsu, Mesopotamia."
Granite (though not as a gemrock) is the state rock of New Hampshire(?) and North Carolina, and one of three rocks designated as the state rocks of Vermont; blue granite is the official state stone of South Carolina; and red granite (also not as a gemrock) is the state stone of Wisconsin. In addition, granite is the state building rock, as contrasted to Plymouth Rock being the state historical rock of Massachusetts
(enamelware) - enamel-coated metal (usually iron or steel, rarely
tin). All sorts of kitchenware, ranging from cookware and
bakeware to tableware (and even bedpans) were made from the mid 1800s
well into the 1900s. The enamel was speckled and baked on the
metal. Some of the dark gray graniteware items that were speckled
roughly resemble granite; although other colors, of which there
were several, did notl, they too were called graniteware in many
quarters. Of the dark gray and white ones that I have seen, those
labeled as made by Kemp Mfg. Co. of Toronto, Ontario, Canada resembled granite most
closely. None, so far as I have been able to
determine was fashioned into anything marketed as granite per se. -
***Wedgewood china - one variety has been made that resembles granite - [Appearance - china is a so-to-speak single phase material.].
REFERENCES: No general reference. Grant, 1955.
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