It is the most widely distributed rock of basic intrusive rocks. Its mineral and chemical composition are characterized by SiO2 content of 45%~52%, K2O+Na2O average of 3.6%±, and iron-magnesium mineral content of 40%-90%. The main minerals are basic plagioclase and monoclinic pyroxene. The minor minerals are olivine, orthopyroxene, brown common hornblende, biotite, and some with a small amount of potassium feldspar and quartz.Dark minerals and light-colored minerals are nearly equal, the former is slightly higher, so it is dark black, the color rate is generally 35% to 70%, the rock has medium to coarse grain structure, and the typical gabbro has girdle structure.
The gabbro is formed by the intrusion of basaltic magma from the deep crust or upper mantle, and is widely distributed in various tectonic environments of the earth's crust and on the moon. The gabbro produced on the moon is characterized by silicon deficiency, alkali, calcium and titanium, and contains cosmic minerals such as bismuth sulphide and natural metallic iron.
The gabbro has a bulk density of 2.8-3.1 g/cm3, a small porosity, a compressive strength of 200-280 MPa, a coarse grain, a high durability, a uniform structure, and sometimes a beautiful pattern, polished. It is very decorative and is often used as a high-grade facing stone.
The size of the gabbro is very large, and the small ones are several or tens of kilometers. They appear in various geological periods, and the larger ones can reach several hundred square kilometers. For example, the “Jinanqing” gabbro in Shandong, which is well-known at home and abroad, belongs to this category. The fresh surface of the rock is dark gray, black gray, radiant and radiant, and the block structure is dominant. The mineral composition is plagioclase, clinopyroxene, olivine, biotite and a small amount of magnetite, a small amount of amphibole, apatite and the like.