Basalt
3 of the 6 encyclopedias on this shelf carry an entry for Basalt. All 3 are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a word said to have been derived from an African word, and to have meant basaltoid syenite, from Ethiopia or upper Egypt. In general the name is given to any trap rock of a black, bluish, or leaden gray color, and possessed of a uniform and compact texture. In a special sense it is a trap rock consisting of augite, feldspar and iron intimately blended, olivine also being not unfrequently present. The augite is the predominant mineral; it is, sometimes, however, exchanged for hornblende, to which it is much akin. The iron is usually magnetic, and is, moreover, often conjoined with titanium. Other minerals are also occasionally present, one being labradorite. It is distinguished from doleryte or dolerite by its possessing chlorine disseminated through it in grains. It is of a very hard, endurable nature, and may be used to advantage in macadamizing roads. The specific gravity of basalt is 3.00. There are fine columnar basalts at the Giant's Causeway in the N. of Ireland; in Scotland at Fingal's Cave and other parts of the Island of Staffa; and along the sides of many hills in the old volcanic district of western and central India. At West Orange, N. J., the face of the First Mountain exhibits basaltic formations, the lines being diagonal and suggesting a huge open fan, with its ribs converging near the ground.
Aiton's Encyclopedia (1910)
a dark, compact, finely grained, igneous rock. It is formed from lava by rapid cooling. It contains usually but little sand, potash, or soda; but is rich in lime, magnesia, and iron. When poured out into sheets, it is apt in cooling to take on what is known as a columnar or basaltic structure. The fluid mass cools into vertical, six-sided columns frequently of great regularity. The process is not essentially different from that which takes place when a mud flat dries and cracks in the sun, except that in the latter case regularity is lacking. The columns of the Giants' Causeway and of Fingal's Cave are familiar examples of a basaltic structure. The cliffs of the Columbia are noted for basaltic columns, as are the Palisades of the Hudson. In California, basalt forms the bottom rock under the gravel in rivers where the largest gold nuggets are found. The table lands of New Mexico and Arizona owe their shape to columns of basalt. See Lava ; Volcano Basaltic columns and balls, Prussian Rhine. Basalt and other eruptive rocks Columns of porphyry, Tyrol. Basalt Granite cliff in Bohemia. Basalt Basaltic columns, Fingal's cave. Basalt Trap rock, Rhone Valley. Basalt Obsidian cliff, Yellowstone Park. Basalt Cannon-ball formation in Bavaria. Basalt
The Encyclopedia of Founding (1892)
A rock of igneous origin, usually of a dark green or blackish color, consisting chiefly of the minerals augite and feldspar, with grains of magnetic or titanic iron. It occurs amorphous, tabular, or globular, but, as in the Giant's Causeway, Ireland, it is usually columnar. See AMORPHOUS. Base-plate. See FOUNDATION-PLATE.
What Has Changed in the Last Century
The three accounts treat basalt as a notable dark rock found at a handful of scenic spots — the Giant's Causeway, Fingal's Cave, the Columbia cliffs. Since then plate tectonics and the ocean-floor surveys of the 1950s and 60s showed that basalt is the commonest rock on Earth, forming essentially the whole of the oceanic crust beneath the sediment, so the columnar showpieces are trivial outcrops of a global layer. The Apollo missions of 1969-72 brought back basalt from the Moon's dark maria, and spacecraft have since found much of the Martian surface to be basaltic as well. Aiton's 1910 comparison of cooling columns to a sun-cracked mud flat is still how the jointing is explained; Collier's terms 'trap rock' and 'doleryte' have largely dropped out of use, dolerite now being distinguished from basalt by coarser grain and intrusive setting rather than by any mineral grains 'disseminated through it'.
Written for this edition, 2026.