The Collaborative International Dictionary of English v.0.48:

Onycha \On"y*cha\, n. [NL., from L. onyx, -ychis, onyx, also, a
   kind of mussel, Gr. ?, ?. See Onyx.]
   [1913 Webster]
   1. An ingredient of the Mosaic incense, probably the
      operculum of some kind of strombus. --Ex. xxx. 34.
      [1913 Webster]

   2. The precious stone called onyx. [R.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Onyx \O"nyx\, n. [L., fr. Gr. ? a claw, finger nail, a veined
   gem. See Nail, and cf. Onycha.]
   1. (Min.) Chalcedony in parallel layers of different shades
      of color. It is used for making cameos, the figure being
      cut in one layer with the next as a ground.
      [1913 Webster]

   2. Same as Mexican onyx.
      [PJC]

   3. A deep jet-black color.
      [PJC]

   Onyx marble, Mexican onyx, a banded variety of marble or
      calcium carbonate resembling onyx. It is obtained from
      Mexico in various colors ranging from white to deep black.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

onyx \o"nyx\, a.
   Deep, jet-black.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

Chalcedony \Chal*ced"o*ny\ (k[a^]l*s[e^]d"[-o]*n[y^] or
   k[a^]l"s[-e]*d[-o]*n[y^]; 277), n.; pl. Chalcedonies
   (-n[i^]z). [ L. chalcedonius, fr. Gr. CHalkhdw`n Chalcedon, a
   town in Asia Minor, opposite to Byzantium: cf. calc['e]doine,
   OE. calcidoine, casidoyne. Cf. Cassidony.] (Min.)
   A cryptocrystalline, translucent variety of quartz, having
   usually a whitish color, and a luster nearly like wax.
   [Written also calcedony.]
   [1913 Webster]

   Note: When chalcedony is variegated with with spots or
         figures, or arranged in differently colored layers, it
         is called agate; and if by reason of the thickness,
         color, and arrangement of the layers it is suitable for
         being carved into cameos, it is called onyx.
         Chrysoprase is green chalcedony; carnelian, a flesh
         red, and sard, a brownish red variety.
         [1913 Webster]

WordNet (r) 3.0 (2006):

onyx
    n 1: a chalcedony with alternating black and white bands; used
         in making cameos

Easton's 1897 Bible Dictionary:

Onyx
   a hail; claw; hoof, (Heb. shoham), a precious stone adorning the
   breast-plate of the high priest and the shoulders of the ephod
   (Ex. 28:9-12, 20; 35:27; Job 28:16; Ezek. 28:13). It was found
   in the land of Havilah (Gen. 2:12). The LXX. translates the
   Hebrew word by smaragdos, an emerald. Some think that the
   sardonyx is meant. But the onyx differs from the sardonyx in
   this, that while the latter has two layers (black and white) the
   former has three (black, white, and red).


U.S. Gazetteer Places (2000):

Onyx, CA -- U.S. Census Designated Place in California
   Population (2000):    476
   Housing Units (2000): 281
   Land area (2000):     11.564076 sq. miles (29.950819 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    11.564076 sq. miles (29.950819 sq. km)
   FIPS code:            53910
   Located within:       California (CA), FIPS 06
   Location:             35.687683 N, 118.217511 W
   ZIP Codes (1990):     93255
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Onyx, CA
    Onyx