Due to its variant nature, the term " gabbro " may be applied loosely to a wide range of intrusive rocks, many of which are merely " gabbroic ".
42.
The Hooggenoeg Formation felsic rocks can be divided into two groups : an intrusive group of interlocking and shallow intrusive rocks, and a porphyritic group of rocks from the veins.
43.
There is a small area of intrusive rock of Devonian age consisting of granite and granodiorite near Paddys Hill and a larger area of similar material of Silurian age at Mount Selwyn.
44.
Of its original nature there is some doubt, but its chemical composition and the occasional presence of porphyritic crystals indicate that it has affinities to the fine-grained acid intrusive rocks.
45.
Textural criteria are less critical in classifying intrusive rocks where the majority of minerals will be visible to the naked eye or at least using a hand lens, magnifying glass or microscope.
46.
Ultramafic intrusive rock hosting nickel bearing sulphides ( pentlandite and mackinawite ) has returned values up to 0.49 % nickel, 38 parts per billion ( ppb ) platinum and 58ppb palladium.
47.
Analysis of intrusive rock microstructures can provide information on source and genesis, including contamination of igneous rocks by wall rocks and identifying crystals which may have been accumulated or dropped out of the melt.
48.
The oldest exposed rocks are Miocene, suggesting that subduction and volcanism began considerably later than in Java and Sumatra to the west, where there are abundant volcanic and intrusive rocks of Late Mesozoic age.
49.
Composed mainly of basaltic alkaline intrusive rocks, this volcano was the result of a major geological upheaval in the tertiary era which were responsible for various volcanic cones in the rocky state of Rio Grande do Norte.
50.
Igneous rocks are formed by the cooling and / or solidification of magma and the formation of a dense network of crystals below the Earth's surface as intrusive rock or on the surface as effusive rock.
