How does obsidian differ from the gabbro?

Question

not sure if everythign is spelled right

Answer 1

Once site points out "You can get away with calling almost any dark, coarse-grained igneous rock gabbro." It's an igneous rock with very little silica (see below) Obsidian is high in silica and really volcanic glass.

"Obsidian consists of about 70 percent or more non-crystallized silica (silicon dioxide). It is chemically similar to granite and rhyolite, which also were originally molten. Because obsidian is not comprised of mineral crystals, technically obsidian is not a true "rock." It is really a congealed liquid with minor amounts of microscopic mineral crystals and rock impurities. Obsidian is relatively soft with a typical hardness of 5 to 5.5 on the mineral hardness scale. In comparison, quartz (crystallized silicon dioxide) has a hardness of 7.0. "

http://volcano.und.edu/vwdocs/vw_hyperex...

Gabbro is a dark, coarse-grained rock that is intrusive and igneous—that is, plutonic, like granite. But unlike granite, gabbro is low in silica and has no quartz;

http://geology.about.com/library/bl/imag...

Obsidian can be used in surgical blades, and is great to make stone arrowheads out of. Gabbro is more what we call "country rock" That is too soft to make good building stone and not pretty enough to polish.

Answer 2

Obsidian is a fine grained rock & gabbro is a much courser grain of rock.  Gabbro can be very impure & may contain some silica, while obsidian is nearly pure silica. Basically, obsidian is glass & was often used by stone aged people to form some very sharp tools & even knives. I almost forgot to add, they are both formed by volcanic activity.

I copied this from Wikipedia... as a I couldn't remember all the composition of Gabbro.

"Gabbro is dense, greenish or dark-colored and contains varied percentages of pyroxene, plagioclase, amphibole, and olivine (olivine gabbro when olivine is present in large quantities).

The pyroxene is mostly clinopyroxene, small amounts of orthopyroxene may be present. If the amount of Orthopyroxene is substantially greater than the amount of clinopyroxene, the rock is then a Norite. Quartz gabbros are also known to occur and are probably derived from magma that was over-saturated with silica. Essexites represent gabbros whose parent magma was under-saturated with silica, resulting in the formation of the feldspathoid mineral nepheline. (Silica saturation of a rock can be evaluated by normative mineralogy). Gabbros contain minor amounts, typically a few percent, of iron-titanium oxides such as magnetite, ilmenite, and ulvospinel."

Answer 3

Anthropology ?

Answer 4

huh?

Answer 5

Gabbro is a coarsely grained igneous rock, the grains set in a ground mass.  The original molten mass cooled slowly enough for crystals to grow (or form) in it.

Obsidian is a glass.  It chills so quickly it  solidified before any crystals formed.  It has no grains.  (Of course most obsidian is not 100% free of crystals.)