Acid igneous rock

The apatite group minerals are the most abundant phosphorus-bearing minerals on Earth, typically as accessory minerals in basic to acidic igneous rocks, pegmatites, hydrothermal veins and cavities, carbonates, contact and regionally metamorphosed rocks, and sedimentary rocks (Deer et al. 1996). The principal members of the apatite group include fluoroapa-tite (Ca5(P04)3F), chloroapatite (Ca5(P04)3Cl), hydroxyapatite, and carbonate apatite (Ca5(P04, C03)3(F,0H)) (Deer et al. 1996). 

Since high-temperature quartz occurring as phenocrysts in acidic igneous rocks (igneous rocks with around 70% SiO content) exclusively take hexagonal bipyra-midal forms with no prismatic faces, it has been assumed that this is the typical... 

The mineral zircon (ZrSi04) occurs in nature as component of acidic igneous rocks. Their weathering yields sediments containing small crystals (sand) of zircon and further heavy minerals. These deposits are resources for industrial production. 

Olivine Nesosilicates Basic and acidic igneous rocks R Source of Fe, Ca, Mg, and Mn unstable in highly leached soil... 

Garnets Nesosilicates High-grade metamorphic/acid igneous rocks R Source of Fe, Mg, Ca, Al, and/or Mn precursor of Fe-oxides... 

The types of substance that are thermoluminescent, either in their natural state or after radiation bombardment, include (112) the alkali metal halides, calcite, dolomite, fluorite, aluminum oxide, magnesium oxide, gypsum, quartz, glass, feldspars, feldspathoids, certain dried clays, and ceramic materials. Of over 3000 rock samples examined for thermoluminescence, some 75% showed visible fight emission (112). Nearly all limestones and acid igneous rocks are naturally thermoluminescent, due mainly to the presence of trace elements of uranium, thorium, and so on. Calcium and magnesium... 

The finest pyroclastic material is called ash. Much more ash is produced on eruption of acidic than basic magmas. Acidic igneous rocks contain over 65% silica, whereas basic igneous rocks contain between 45 and 55%. Those rocks that have a silica content between acid and basic are referred to as intermediate, and those with less than 45% silica are termed ultrabasic. As mentioned, the reason for the difference in explosivity is because acidic material is more viscous than basic or basaltic lava. 

Hornblendes are dark green or greenish black amphibole group minerals with compositions which vary about Ca2(Mg,Fe, Al)5(Al,Si)g022(OH)2. Those varieties containing more iron are darker in colour. Hornblendes are widespread minerals and are common in intermediate and acid igneous rocks as well as regionally metamorphosed basic rocks. 

Nagasawa (1971) measured Eu anomalies in coexisting Ca-feldspars and K-feldspars (two distinct minerals) from acid igneous rocks. He concluded that Eu(II) was present, that it behaved very much like Sr(Il), and that the method of Philpotts (1970) for estimating concentration ratios of Eu(II) to Eu(III) should be reasonable. 

Uranium, thorium and potassium content varies with rock type and shows increasing radioactive heat generation from basic to acid igneous rocks. This tendency is also reflected in empirical equations correlating heat generation and density and seismic velocity, because both parameters increase from acid to basic t5q>es. Examples are given in Table 5.12 ... 

---