How to classify igneous rocks into ultramafic, mafic. If we combine texturecooling history and color composition in a grid we get the classification in the table below. The color is considered light if there is little iron or magnesium felsic minerals. The entire area contains many nephelinebearing dike rocks, but almost all are gray or pink or even red due to the color in the felsics. The term is a portmanteau, made up from magnesium and ferric mafic minerals are usually dark in color and have a specific gravity greater than 3. Of the oxides, silica sio 2 is usually the most abundant. The classification chart above shows how these characteristics are used to. Common felsic minerals include quartz, muscovite mica, and the orthoclase feldspars. Others may be soft in the ground, but they harden once they spend time in the air. Geologists sometimes find it useful to classify igneous rocks based on color. Pough this book has many color pictures of 250 common gems, ores and other rocks and minerals in a paperback size book 3 34x 7. Mafic is used for silicate minerals, magmas, and rocks which are relatively.
The most common felsic rock is granite, which represents the purified end product of the earths internal differentiation process. Jul 17, 2017 dip the very end of a stiff paint brush into the second paint color and then splatter and speckle the second paint color onto the rock, producing tiny specks of the second color. Therefore, rocks are divided into ultramafic, mafic, intermediate, and felsic. Felsic rocks are light in color, intermediate rocks have varying gray colors, and mafic rocks are dark in color. Felsic and mafic rocks, division of igneous rocks on the basis of their silica content. Be sure to define the terms in italics in your notes. Part a identification of igneous rocks classification of igneous rocks is based on texture grain size and mineral composition often related to color. Felsic rocks are usually light in color and have specific gravities less than 3. Felsic rocks tend to be light in color white, pink, tan, light brown, light gray. Bk2 rocks and minerals peterson first guides by frederick h. The color index of an igneous rock is a measure of the ratio of dark colored, or mafic, minerals to light colored, or felsic, minerals. Mafic is an adjective describing a silicate mineral or igneous rock which is rich in magnesium and iron. Mafic rocks have between 45 and 55% of silica, whereas felsic rocks have over 65% of silica, the highest of all types.
Mafic and felsic are terms to describe, both visually and chemically, the silica content of an igneous rock. Use the classification chart table 1 to assign correct names to the lab specimens. The color of the rocks and sizes of the crystals are your clues. An easy method of determining the igneous rock composition is by determining the percentage of darkcolored minerals in the rock, without trying to identify the actual minerals present. Basalt, which is mafic, tends to be solid, dark, and rough in color. Then determine the texture of the rock and based on the two, identify t he rock name. Due to the color of the minerals forming them, the rocks are either light or dark. Igneous rocks are rocks formed by the cooling and setting of molten rock. These are your white and pink colored igneous rocks. An igneous rock with a large amount of nonferromagnesian minerals will be light in color, such as the silicic or felsic rocks fel from feldspar, and sic from silicarich quartz. They have a higher silica content and a lower iron and magnesium content. My son loves to color these while i am reading to him about the pictured item. Identify the rocks in the study set using the rock identification chart.
This is the rock type that is found in oceanic crust. Flash cards for geol 110l lab with depriest at tennesseemartin utm. We might also classify rocks according to whether they contain felsic or mafic minerals, and as we shall see this is a good way to classify certain rocks. Within these four groups, rocks are named depending on whether they display coarsegrained or finegrained textures. Felsic magma or lava is higher in viscosity than mafic magmalava. Most mafic minerals are dark in color, and common rockforming mafic minerals include olivine, pyroxene, amphibole, and biotite. Historical geologyrocks wikibooks, open books for an open. As a result it is characteristically olivegreens in color. Summary igneous rocks are classified first by composition.
Igneous rocks pictures of intrusive and extrusive rock types. Felsic magma is molten rock magma with a high concentration of silica, sodium and potassium these are common together as opposed to a mafic dark magma, which is typically richer in iron, magnesium and calcium. Slow cooling allows time for large crystals to form, so intrusive igneous rocks have. Calcalkaline rocks, felsic rocks, intermediate rocks, mafic rocks, ultramafic rocks, ultrapotassic rocks. Minerals form when atoms bond together in a crystalline arrangement. Mineralogic contents felsic rock, with predominance of quartz, alkali feldspar andor feldspathoids. Felsic color, a bunch of quartz, potassium feldspar, very few dark minerals found.
The colorcomposition of a rock may be divided into dark colored rocks mafic, intermediate colored rocks intermediate, and light colored rocks felsic. Igneous rocks are classified based on only 4 colors. To identify name igneous rocks, you determine two things about the rock. Chemical analyses of the most abundant components in rocks usually are presented as oxides of the elements. Name the 2 factors that affect the composition of igneous rocks. Mafic rocks are darker and are composed of magnesium and iron.
It has a composition that is intermediate between rhyolite and andesite. Monzonite is an intermediate igneous intrusive rock composed of approximately equal. But the most fundamental way in which geologists classify rocks is to label them as igneous, sedimentary, or metamorphic. Igneous rocks introduction textures composition be sure to. The color composition of a rock may be divided into dark colored rocks mafic, intermediate colored rocks intermediate, and light colored rocks felsic.
Mafic is an adjective describing a silicate mineral or igneous rock that is rich in magnesium and iron, and is thus a portmanteau of magnesium and ferric. Explore and color in the amazing world of minerals and crystals. Volcanic rocks of early proterozoic greenstone belts, k. A book of the names and address of people living in a city. So, based on color alone, weve been able to start classifying the igneous rocks. The word felsic was made up from parts of those words. Mafic rocks have about 50 percent silica and high amounts of iron, magnesium, and calcium and are dark in color. If oceanic crust is melted, then a rock rich in darksilicate minerals. Felsic book of the names and address of people living in a city.
Resources alaska department of natural resources, 2010, division of geological and. Black minerals are primarily amphibole like hornblende and plagioclase feldspar. Dec 24, 2016 mafic and felsic are terms to describe, both visually and chemically, the silica content of an igneous rock. The rocks will be dark in color, somewhat heavier than granitic rocks and devoid of quartz. An igneous rock at the boundary between the mafic and ultramafic fields. What is the different in composition between a dacite and an andesite. As a first attempt at classifying rock compositions based on color, most students end up with three lightcolored rocks felsic, two intermediate. Felsic rock synonyms, felsic rock pronunciation, felsic rock translation, english dictionary definition of felsic rock. Mafic rock is commonly contrasted with felsic rock, in which lightcoloured minerals predominate. Learn about the many interesting facts, uses, and properties of rocks and minerals, as well as helpful guidance on starting, building and maintaining your own rock and mineral collection. If we combine texturecooling history and colorcomposition in a grid we get the classification in the table below. Historical geologyrocks wikibooks, open books for an. This book is good for its description of the rocks and minerals, but lets face it, coloring rocks isnt as exciting as going out and finding them.
As has already been described, igneous rocks are classified into four categories, based on either their chemistry or their mineral composition. Felsic rocks are rich in silica, potassium, sodium, and aluminum and contain only small amounts of iron, magnesium, and calcium. Felsic rocks are igneous rocks that are rich in feldspar and silicon. The color distinction comes from the differences in iron and magnesium content. How are felsic, intermediate and mafic igneous rocks different. In these cases, the color of a rock becomes helpful. Minerals and rocks with a composition in between mafic and felsic are called intermediate. Felsic, intermediate and mafic igneous rocks differ in their mineral composition. Jul 31, 2019 metamorphic rocks are formed when igneous and sedimentary rocks are changed by intense heat or pressure.
Mafic simple english wikipedia, the free encyclopedia. A rock that is considered intermediate between the mafic and felsic rocks is truly an intermediate in terms of the color and mineral composition. Common mafic rocks include basalt, diabase and gabbro. Mafic rock, in geology, igneous rock that is dominated by the silicates pyroxene, amphibole, olivine, and mica. Dip the very end of a stiff paint brush into the second paint color and then splatter and speckle the second paint color onto the rock, producing tiny specks of the second color. Felsic rocks have a higher silica content 65% to 75%, so they are generally harder, lighter in color, are enriched in elements such as s. Felsic also called silicic igneous rocks have a lower density, and are generally lighter in color white, tan, pink.
Because color is sensitive to minor chemical differences it is not a very reliable index to the history or composition of any given rock. Peridotite intrusive peridotite or dunite is composed of 90100% olivine. Colour index, in igneous petrology, the sum of the volume percentages of the coloured, or dark, minerals contained by the rock. Mafic rocks tend to be dark in color black, very dark brown, very dark gray, dark green mixed with black. Intermediate rocks are composed of the minerals amphibole and feldspar and contain a combination of light and dark minerals. For large sections of rocks, left in place, use a paint sprayer to apply the latex exterior paint. Felsic rocks are light colored because they contain light. As ironrich silicates are normally dark in color, mafic rocks are darkcolored. Dacite is a finegrained, extrusive igneous rock that is usually light in color. Condie editor, proterozoic crustal evolution, elsevier, page 35. Felsic rock definition of felsic rock by the free dictionary. The students will be able to classify igneous rocks according to origin, texture, and color. Marble from limestone, a sedimentary rock and granulite from basalt, an igneous rock are examples of metamorphic rocks. The color index of igneous rocks is a very useful indicator of the types of minerals present in the rock and therefore the specific type of rock.
They are extremely detailed and educational, but even my 6 year old loves to color them. These terms felsic, intermediate, mafic, ultramafic correspond to the type of magma a rock comes from each composition type has an extrusiveintrusive equivalent the composition felsic, intermediate, mafic, ultramafic also corresponds to which minerals are in the assoicated rock felsic rocks contain more nonferromagnesian light. Felsic rocks are light in color and are composed of feldspars and silicates. Ultramafic rocks are dominated by olivine andor pyroxene mafic rocks are dominated by plagioclase and pyroxene even if you cant 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. Felsic rocks are mostly feldspar especially kfeldspar, at least 10% quartz, and less than 15% mafic minerals biotite, hornblende. Mafic rocks often also contain calciumrich varieties of. Some common rocks can be scratched with your fingernails such as shale, soapstone, gypsum rock, and peat. Felsic rocks most often appear white, light gray, or pink. Extrusive rock types cliffsnotes study guides book. Oct 27, 2015 generally as the percentage of felsic minerals. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. Unlike mafic rocks, which are rocks high in magnesium and iron. How are felsic, intermediate and mafic igneous rocks. These minerals are high in magnesium and ferric oxides, and their presence gives mafic rock its characteristic dark colour.
Common rockforming mafic minerals include olivine, pyroxene, amphibole, biotite and other micas, augite and the calciumrich plagioclase. Felsic igneous rocks, as a whole rock, tend to have light colors or shades. Then determine the texture of the rock and based on the two. Relating to or containing a group of lightcolored silicate minerals that occur in igneous rocks, including minerals of the feldspathoid group and the. Volume percentages, accurate to within 1 percent, can be estimated under the microscope by using a pointcounting technique over a plane section of the rock. Felsic rocks are lightcolored because they contain light silicate minerals such as quartz, potassium feldspar, muscovite mica, and sodiumrich feldspar minerals. Mafic igneous rocks, on the whole, tend to be dark. Felsic minerals are usually light in color and have specific gravities less than 3. First determine composition, which is based on mineral content or color, if you cant see minerals.