Early in gestation the fetal heart rate is predominately under the control of the sympathetic nervous system and arterial chemoreceptors [1]. As the fetus develops its heart rate decreases in response to parasympathetic ( vagal stimulation) nervous system maturation and variability becomes more pronounced [2].
Igneous Rocks by Composition Igneous rocks are classified according to their mineral content: Ultramafic rocks are dominated by olivine and/or pyroxene. Mafic rocks are dominated by plagioclase and pyroxene (even if you can't see them with the naked eye) and smaller amounts of olivine.Intermediate rocks are roughly even mixtures of felsic minerals (mainly plagioclase) and mafic minerals (mainly hornblende, pyroxene, and/or biotite).There is little or no quartz. Felsic rocks are mostly feldspar (especially K-feldspar), at least 10% quartz, and less than 15% mafic minerals (biotite, hornblende).afic rocks are dominated by plagioclase and pyroxene (even if you can't see them with the naked eye) and smaller amounts of olivine. Intermediate rocks are roughly even mixtures of felsic minerals (mainly plagioclase) and mafic minerals (mainly hornblende, pyroxene, and/or biotite).
Examples of intrusive rocks are granite and gabbro. Granite is made up of three common minerals - quartz, mica and feldspar - and when viewed from a distance appear tan, pinkish or gray, depending on the concentrations and grain sizes of the three minerals. This rock is very widely used as a building material, due to its abundance and strength. Gabbro has a lower quartz content than granite, and is therefore much darker. Liquid rock that reaches the surface cools very quickly. As a result of this immediate cooling, the crystals produced are extremely small.