The Collaborative International Dictionary of English v.0.48:

Basalt \Ba*salt"\, n. [L. basaltes (an African word), a dark and
   hard species of marble found in Ethiopia: cf. F. basalte.]
   1. (Geol.) A rock of igneous origin, consisting of augite and
      triclinic feldspar, with grains of magnetic or titanic
      iron, and also bottle-green particles of olivine
      frequently disseminated.
      [1913 Webster]

   Note: It is usually of a greenish black color, or of some
         dull brown shade, or black. It constitutes immense beds
         in some regions, and also occurs in veins or dikes
         cutting through other rocks. It has often a prismatic
         structure as at the Giant's Causeway, in Ireland, where
         the columns are as regular as if the work of art. It is
         a very tough and heavy rock, and is one of the best
         materials for macadamizing roads.
         [1913 Webster]

   2. An imitation, in pottery, of natural basalt; a kind of
      black porcelain.
      [1913 Webster]

WordNet (r) 3.0 (2006):

basalt
    n 1: the commonest type of solidified lava; a dense dark grey
         fine-grained igneous rock that is composed chiefly of
         plagioclase feldspar and pyroxene

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "basalt":
   aa, abyssal rock, bedrock, block lava, brash, breccia,
   conglomerate, crag, druid stone, festooned pahoehoe, gneiss,
   granite, igneous rock, lava, limestone, living rock, magma,
   mantlerock, metamorphic rock, monolith, pahoehoe, pillow lava,
   porphyry, pudding stone, regolith, rock, ropy lava, rubble,
   rubblestone, sandstone, sarsen, schist, scoria, scree,
   sedimentary rock, shelly pahoehoe, stone, talus, tufa, tuff



U.S. Gazetteer Places (2000):

Basalt, CO -- U.S. town in Colorado
   Population (2000):    2681
   Housing Units (2000): 1218
   Land area (2000):     1.922180 sq. miles (4.978423 sq. km)
   Water area (2000):    0.018520 sq. miles (0.047967 sq. km)
   Total area (2000):    1.940700 sq. miles (5.026390 sq. km)
   FIPS code:            04935
   Located within:       Colorado (CO), FIPS 08
   Location:             39.368382 N, 107.038263 W
   ZIP Codes (1990):     81621
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Basalt, CO
    Basalt


U.S. Gazetteer Places (2000):

Basalt, ID -- U.S. city in Idaho
   Population (2000):    419
   Housing Units (2000): 133
   Land area (2000):     0.287416 sq. miles (0.744405 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.287416 sq. miles (0.744405 sq. km)
   FIPS code:            05230
   Located within:       Idaho (ID), FIPS 16
   Location:             43.314270 N, 112.163571 W
   ZIP Codes (1990):
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Basalt, ID
    Basalt