Agata Negra (black agate) - misnomer sometimes used in the marketplace.

Apache tears - dark gray to nearly black, pebble-sized glass nodules, most of which have greatest dimensions ranging  between two and four centimeters, that occur as remnants within or weathered out of light gray perlite.  (Perlite, apparently derived from obsidian as the result of hydration involving meteoric water, is a light gray rock made up of concentrically fractured fragments.)  Many apache tears in the marketplace are from Maricopa and Pinal counties, Arizona.

Banded obsidian - the banding commonly exhibits a flowlike appearance;  some roughly banded obsidian has been incorrectly designated onyx obsidian. 
 

Black lava glass -  descriptive name given to some obsidian.

Colombianite (americanite) - a variety of obsidian from the vicinity of Cali, Colombia.

Chatoyant obsidian - name sometimes applied to varieties that are iridescent in diverse colors;  appearance is apparently due to the presence of minute inclusions and/or bubbles.

Desert glass - name sometimes applied a pale yellow glass that some people have identified as obsidian but seems more likely to be an impactite glass-- e.g., that from Libya.  This term is further confounded because it also has been applied to the amethyst-colored man-made glass frequently found in sandy areas, such as deserts and on beaches, with its purple color apparently developed as a result of exposure of essentially colorless glass to ultraviolet or cosmic rays from the sun.  See TECTITE entry.
 

Electric blue obsidian - obsidian with a vibrant blue color.

Fire obsidian - iridescent obsidian from Glass Buttes, Oregon;  "fire" is said to be due to reflection of light off thin layers the refractive indices of which are higher than the rest of the obsidian because of their containing extremely small (nanometric) magnetite crystals (Rossman and Miller, 2007).
 

Flame obsidian - another name for fire obsidian.

Flowering obsidian - similar to snowflake obsidian.

Glass (or glassy) lava - overall term that has been used, especially in the field.

Glass agate - atrocious misnomer sometimes given obsidian.

Golden sheen obsidian (also gold or golden obsidian) - name widely given in the marketplace to sheen obsidian (q.v.) with the precominant "sheen" a golden brown color (see Fig. E).
 

Iceland agate (or Iceland agate lava) - misnomer sometimes given to a brownish or grayish variety of obsidian from Iceland.

Iris obsidian - another name for rainbow obsidian.

Itatli - obsidian (Aztec).

Iztli - obsidian (Aztec).

Lassenite - glass of trachytic composition (trachyte is the aphanitic equivalent of syenite, which is composed of 90 or more percent of alkali feldspar) from the vicinity of Lassen Peak, California.

Libyan glass - see Desert glass.

Mahogany obsidian (also Mountain mahogany) - reddish subtranslucent obsidian, commonly including black or gray bandlike or streaked swirl-like patterns.  See Fig. A.
 

Marekanite - name for Apache tearlike masses OR, according to some ambiguous statements, a mottled brown and black obsidian from the vicinity of the Marekanka River, which flows into the Sea of Okhotsk, off eastern Siberia.

Marskanite - name  applied variously -- e.g., to mottled brown and black obsidian from Siberia;   to any cloudy, smoky gray obsidian;  and to brown and gray, commonly in part  yellowish or reddish, obsidian (especially those from Mexico).

Mexican 'Mayan' - see Rainbow obsidian.

Mount Saint Helens emerald - a misleading misnomer given obsidian (and even more often to a green glass produced by melting ash erupted by Mount St. Helens.
 

Montana jet - a misleading misnomer given some black obsidian from the Yellowstone National Park area, Wyoming.

Mountain mahogany - See Mahogany obsidian.
 

Nevada diamond - term that has been applied, albeit rarely, to what is said to be artificially decolorized obsidian.

Obsidian "cat's-eye" (or "cat's eye obsidian) - name sometimes given to obsidian that has a golden chatoyant-like appearance;  see Golden sheen obsidian.

Obsidianite - name introduced by Walcott (1898) for what are now known to be tektites (australites) from Australia;  however, according to Bates and Jackson (1987) this term came to have wider usage, and "Most stones originally described as 'obsidianite' were later shown to be true obsidian and not tektites." [To date, however, I have not found examples to document this purported later, wider usage.]

Onyx obsidian - term sometimes applied to banded obsidian.

Peanut obsidian - a gray to greenish gray perlite that contains red or brownish red stellate spherulites, which consist of radiating fibers of hematite-stained feldspar within shells of chalcedony;  the overall appearance -- both color- and size-wise -- roughly resembles a mass of peanuts.  A noteworthy occurrence is near Alamos, State of Sonora, Mexico.

Pearlylite - name sometimes given in the marketplace to obsidian in jewelry.

Pitchstone - obsidian that has a pitchlike luster.  This rock apprently  represents an intermediate phase in devitrification of the precursor obsidian per se;  among other things, it contains more water and is less brittle than typical obsidians.

Plum obsidian - obsidian with a plum (purplish) color.

Pumpkin obsidian - obsidian with a pumpkin-orange color.
 

Porphyritic obsidian - obsidian containing sporadic phenocrysts.

Rainbow obsidian (also rainbow sheen obsidian and iris obsidian) - obsidian that exhibits a multicolored iridescence, apparently because of the presence of inclusions -- e.g., that from Glass Buttes, Lake County, Oregon and that, called Mexican 'Mayan'  from the state of Jalisco, Mexico (see Koivula, Kammerling and Fritsch, 1993).  See Fig. C.
 

Royal agate - misnomer sometimes applied to mottled obsidian.
 

Rhyolite glass - name apparently given by someone who knew that most obsidian is chemically like rhyolite but did not know that rhyolite is an aphanitic rock consisting only in part of glass.

Royal blue obsidian - a bluish obsidian from northeastern California.

Schiller obsidian - obsidian exhibiting a schiller effect.

Sheen obsidian - obsidian that exhibits a sheen when rotated in reflected light;  many marketers distinguish diverse "sheen obsidians" by directing attention to the color of their sheen -- e.g., golden ... , silver ..., and even rainbow sheen obsidian.

Snowflake obsidian (also spherulitic obsidian and flowering obsidian) - dark gray to nearly black obsidian with inclusions of white, gray or rarely red spherulites, which in many specimens have been identified as cristobalite (a high-temperature polymorph of silica). Fine examples of  this obsidian occur near Milford, Beaver County, Utah.  See Fig. B.
 

"Star" obsidian (also "starred Apache tear obsidian") - misnomer -- in that no asterism is apparent -- applied in the marketplace to gemstones cut from aventurescent (hematite- and ilmenite-bearing) obsidian, most of which occur as Apache tears (see Koivula & Tannous, 2003).

Velvet obsidian - obsidian with a velvetlike appeareance.
 

Volcanic glass - geological designation sometimes applied to obsidian used as a gemrock.

Xaga - name used for obsidian by some native Americans from California. The Pomo Indians are said to have distinguished between hard obsidian, which they called dupa xaga and used for razors etc. and less hard obsidian, which they called bati xaga.