Why are mafic minerals are in sedimentary rocks

What processes normally take place in the transformation of sediments to sedimentary rock? What are the processes that lead to the formation of a metamorphic rock? What must happen within a magma chamber for fractional crystallization to take place? Explain the difference between aphanitic and phaneritic textures. Explain the difference between porphyritic and pegmatitic textures. Why does a dyke commonly have a fine-grained margin? What is the difference between a batholith and a stock?

Describe two ways in which batholiths intrude into existing rock. Why is compositional layering a common feature of mafic plutons but not of felsic plutons? Previous: 3. Next: Chapter 4 Volcanism. Sedimentary rock formed from clay-size particles too small to be seen with a light microscope are called shale. Rock formed from silt-size particles visible under a microscope are called siltstone.

Rock formed from these are called sandstone. Limestone , a carbonate rock, is formed from the biogenic or physical precipitation of calcite CaCO 3 directly from calcium and bicarbonate ions dissolved in water solution.

The calcite is most commonly formed as shells of marine organisms of visible or microscopic size. Much limestone has apparently been altered over the ages into a related carbonate rock dolomite , which is a calcium magnesium carbonate Ca Mg CO 3 2. There the rock re-crystallizes very slowly while remaining in the solid state, forming new minerals that are stable under the high temperature and pressure conditions. If there are platy or elongate minerals in the resulting metamorphic rock they will show a preferred alignment or foliation.

Foliated Metamorphic Rocks Slate is a hard, very fine-grained rock with a well-developed rock cleavage caused by the incipient growth of platy micaceous minerals, due to metamorphism of fine-grained clastic sediments such as shale.

Principal mineral is typically clay. Principal minerals are typically visible micas with some invisible clays. Gneiss is a medium to coarse-grained, irregularly banded rock with only poorly developed cleavage. The light and dark bands are alternations of felsic vs. Felsic minerals are usually light in color and have specific gravities less than 3. Common felsic minerals include quartz, muscovite mica, and the orthoclase feldspars.

The most common felsic rock is granite , which represents the purified end product of the earth's internal differentiation process. It is important to note that there are many intermediate steps in the purification process, and many intermediate magmas which are produced during the conversion from mafic to felsic.

We call the magmas associated with these intermediate stages "intermediate.