BASALT

( Fr- basalte; Ger- Basalt; Nor- basalt; Rus- )

BASALT (see also PORPHYRY entry)

A. Basalt slice (greatest dimension - 7 cm) with chiefly potassium feldspar amygdules from Keweenawan Peninsula, Michigan.  R.V. Dietrich collection. (© photo by Dick Dietrich)

B. Basalt ceremonial jaguar metate (height - 14.6 cm) from Costa Rica.  As noted on the Barakat Gallery web site (www.barakatgallery.com): "One crucial aspect of Meso-American sculpture is the image of jaguar.  In Costa Rica, jaguars were considered as a powerful god and their images were often used . . ." Pre-Columbian (700 -1000 AD) collection, Barakat Gallery, Beverly Hills, California. (© photo courtesy of Victor Barakat)

C. Basalt "Sitting Woman" carving (height -18.8 cm) by the late Paul Toolooktook of the Baker Lake Community, Nunavut.  Eskimo Art Gallery, Toronto, Ontario, Canada.  (© photo courtesy Eskimo Art Gallery, www.eskimoart.com)

DESCRIPTION: Basalt is an aphanitic igneous rock that, with a petrographic microscope, can be seen to consist largely of a dark colored pyroxene and a light to medium dark colored plagioclase feldspar with or without minor amounts of glass.
    Color - typically dark gray to black
    H. > 5½ - 6 (on basis of hardness values of constituent minerals), the lesser value if relatively large percentages of glass are present
    S.G. 2.7-3.1
    Light transmission - opaque
    Breakage - subconchoidal fracture, commonly yielding grainy surfaces
    Miscellany - some basalts used as gemrocks are amygdaloidal; commonly, the amygdules consist of one or more minerals of diverse colors that contrast markedly with the dark gray to black overall color of the basalt.  A so-to-speak special basalt that is used as a gemrock is porphyritic with off-white phenocrysts surrounded by a dark gray to nearly black groundmass (see LEOPARD ROCKS entry).

OTHER NAMES: Basalt is the accepted petrographic designation for this rock, which is the aphanitic equivalent of gabbro. Some individual masses of basalt and also some groups of these masses have been given formal geological names. Examples are the Cape Foulweather Basalt and the Picture Gorge Basalt of the Columbia River Basalts of the Columbia River Plateau region of Washington, Oregon and Idaho. Designations such as these are used widely in the geological literature and on geological maps.  Unfortunately, several rocks recorded as basalts (especially by archeologists) are other aphanitic rocks -- e.g., andesites -- with occurrences similar to those of basalt.  The following names have been applied to some of the basalts utilized as gemrocks.

USES: The widespread occurrence of basalt masses, sizeable pieces of which have an overall homogeneity of color and other desirable characteristics, led to the early use of basalt for fashioning artifacts, which have been found on all continents except Antarctica and also on several Pacific and Caribbean islands. Among the artifacts recorded are weapons, tools, and diverse sculpted and carved pieces -- e.g., spearheads; adzes and scrapers; columns, bas reliefs, statues, statuettes, and manos and metates (the last two used for grinding corn and other grains and also in religious ceremonies). In addition, "more compact pieces ... were used for scarabs and intagli by the ... Egyptians. [And,] It is not unusual to find Gnostic amulets, belonging to the Alexandrian sects, engraved in Basalt." (King 1865, p.123)

Today, basalt continues to be used by sculptors and carvers who fashion pieces most of which are sold as decorative articles ranging from relatively inexpensive souvenirs to objets d'art with price tags of tens of thousands of dollars. In addition, basalt cut into rectilinear prisms and other relatively simple geometric solids has found rather widespread use as paper weights and bookends. Also, albeit rather rarely, basalt has been cut and polished to form, for example, cabochons for mounting in pendants and other jewelry.

OCCURRENCES: Widespread, especially in areas of so-called plateau basalts, such as the aforementioned Columbia River basalts of Washington, Oregon and Idaho and the Deccan Traps of southern India;  also in less extensive volcanic terrains, typically as relatively small masses such as volcanic necks, dikes, and sills -- many of which consist in part of genetically related diabase, dolerite or microgabbro. Examples of the latter are common among the rocks comprising the Pacific "ring of fire" and the included "hot spots" (e.g., the Hawaiian islands) and also as the igneous components of the Mesozoic basins of Connecticut, New York, New Jersey, Virginia, and North Carolina.

NOTEWORTHY LOCALITIES: See information under preceding subheading. Also, from an historic viewpoint, a friend said I should mention the "fact" that from an archeological standpoint the so-called Tautama lode -- a quarry, on Pitcairn -- was apparently the source of most, if not all, of the fine-grained basalt artifacts found in Polynesia. (I have not verified this "fact.")

REMARKS:  The designation basalt apparently stems to the Latin basaltes, about which OED (1889 ed.) notes "(originally an African word, Pliny)."

The celebrated Rosetta stone -- which provided the key Champollion, the French linguist, used to decipher ancient Egyptian hieroglyphics -- is a basalt stele that was found near Rosetta (Rashid), near the western mouth of the Nile, in 1799, during Napoleon's occupation of Egypt. This basalt slab is now in the Royal British Museum in London.

A fine example of the early use of basalt by sculptors is the Goddess Kubaba bas relief (83 x 37 cm), which dates to the Late Hittite Principalities period (9th century B.C.). The goddess' features, her headdress, and the pomegranate in her right hand inter alia exhibit  remarkable detail.  This bas relief, currently in the Anatolian Civilizations Museum, Ankara, Turkey, is pictured on a postage stamp of the “Historical Works Series” issued in 1966 by the Turkey Monetary Postal Administration.    In addition, many so-to-speak curio size articles fashioned from basalt, which represent several different cultures, have been found in many places the world over -- e.g., the diverse artifacts associated with the ancient Maori, Olmec, and Inuit.   And, some present day Maori and Inuit continue to sculpt and carve basalt items that  are marketed rather widely. (Several additional pieces made from basalt can be seen by searching the internet using "basalt" and, if one's interest is geographical, merely add the name of  the continent and/or country.)

The aforementioned use of rather commonplace prisms (etc.) as paper weights and bookends depends largely on  the relatively high specific gravity of basalt.  But, an added benefit accrues, especially so far as it use as a paper weight, because the typically dark gray to nearly black in color of basalt contrasts markedly with that of the papers to be held in place.

SIMULANT:

***Wedgwood black basalt (also called Egyptian ware and basaltes ware) – this black unglazed stoneware, developed in the late 1750s by Josiah Wedgwood [1730-1795],  has been used for boxes (e.g., decorative cylindrical cigarette holders), candlesticks, jugs, tea pots and creamers, vases, and, especially since the mid-20th century, as busts of historical figures (e.g., the Dwight D. Eisenhower "issue") and  medallions. - [Appearance is sufficient in nearly all cases. Additionally, virtually all Wedgwood pieces have the Wedgwood mark somewhere on their bases.].

REFERENCES: No general reference.

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Last update: 23 May 2005
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