Laboratory # 1 Minerals and Rocks

Bring to lab: Hand lens, notebook and your textbook.

Read chapter 3, 4, 5, and 6.

Purpose: The purpose of this lab is to give you some familiarity with the most common rock forming minerals, common rock types and common fossils.

Part A: Minerals

Read through the physical properties of minerals (handouts and your textbook Chapter 3, page 51-73) to get a feeling for some of the common tests used to discriminate between the common rock-forming minerals.

There are 34 minerals in the reference set in the lab. There is a key that tells the names of each mineral in the set. For the even-numbered minerals select three physical properties you believe are the most useful in keying these minerals. At the end of the lab (two weeks from today) turn in a list of the even-numbered minerals with their three physical properties that you think are useful in identifying each mineral. (This is not going to be graded)

After you studied the most common rock forming minerals take the "quiz Lab 1" on Moodle.

Part B: Rocks

Examine the handouts (given in class) on naming igneous, sedimentary, and metamorphic rocks. Also, refer to chapters 4, 5, and 6 in your textbook. Take some time to examine the rock examples available to you in the back of the room. These rocks are keyed to your handouts. Try to decide why these rocks are classified the way they are.

At the end of the lab (two weeks from the 1st day), identify all the unknown rocks.

After you studied the three types of rocks take the "quiz Lab 2"

Determinative Properties of minerals

When we look at a mineral and describe it we are actually noting its physical properties. It is these properties that allow us to identify the mineral. Understanding the main physical properties of minerals and being able to recognize them, is therefore an important skill to develop in geology. The physical properties most commonly used in mineral identification are: color, streak, luster, cleavages, hardness and specific gravity. Other testes such as magnetism and reaction to HCl are used to identify specific minerals. Read about the physical properties before lab and then study the example set in the lab before moving on to exercise.

Rocks:
Igneous rocks:
Igneous rocks form by crystallization of magma, which originates through partial melting of the earth's mantle or deep crust under extremely high temperature conditions. When the magma crystallizes below the surface of the earth it forms intrusive or plutonic igneous rocks that have coarse grains of minerals. When the magma solidify at the surface it forms extrusive or volcanic rocks with fine grained minerals.

The rocks displayed by the window will give you a better perspective on igneous rocks. They are arranged by composition, from silicic to mafic, in the same way as the rock classification scheme. Note the general differences in color from the silicic end to the mafic end. Note also the exceptions. Nature usually does not divide things into tidy boxes like the ones we have in the lab for you. The textures, compositions and colors or rock are gradational. When great accuracy is needed in rock identification, the geologist relies on thin-section examination or other sophisticated techniques such as X-ray fluorescence, X-ray diffraction and electron microprobe analysis. We have set up a petrographic microscope at the back of the lab with thin-sections of several of the rocks. If you are interested, ask one of the lab assistant to explain how the microscope works and how to identify the minerals.. Study each of these examples.

Igneous rock identification:
Description of a rock, including details of its texture and mineralogy, is an absolute prerequisite to rock identification. The name that is finally assigned to the rock is much less important than this complete description. A uniform system of rock classification is useful, however, in that it allows earth scientists to communicate with each other. The igneous rock classification scheme we will be using is similar to classification of systems used by petrologists all over the world.

For today's lab study the igneous rock classification on display. Both texture and minerals are used when naming igneous rocks. The texture should tell you whether the rock is volcanic or plutonic. The minerals will tell you the approximate composition. This handout cover most common igneous rocks. When a geologist names a rock, he or she wants a name more specific than just a "basalt" or "granite" if possible. Therefore, before the rock name, the names of the mafic (dark) minerals in the rock are listed. For example, if biotite and hornblende are present in a granite, the full rock name is "biotite, hornblende granite". This name distinguishes the above rock from a biotite granite which lucks hornblende. The minerals used in this way are biotite, hornblende (amphibole) augite (pyroxene) and olivine.

Look at the igneous rocks on display and familiarize yourself with some of the different varieties.

Metamorphic rocks:
Metamorphic rocks are produce by conversion, in the solid state of some preexisting igneous, sedimentary or metamorphic rock. Metamorphic changes are brought about when the parent rock is subjected to temperature, pressure that are different from the temperature and pressure of formation. In a hand specimen or an outcrop, the most striking characteristic that stamps the rock as metamorphic is usually its fabric. Metamorphic rocks typically are foliated (schistose or gneissose), lineated, or in rocks adjacent to igneous contacts, spotted or hornfelsic.

Foliation is a planar fabric produced in metamorphic rocks through deformation and crystal growth. A foliation can be formed or defined by tabular, platy or elongate crystals, which are all aligned parallel to the plane of the foliation in the rock. Technically, the parallelism of the crystals is called grain shape preferred orientation, and when the fabric is dominantly defined by mica, it can be called schistocity. A foliation can also be defined by planar bands of material of differing composition (technically, this occurs in almost all sedimentary rocks); this is called a gneissose foliation.

Look at the metamorphic rocks on display and familiarize yourself with some of the varieties and non-foliated metamorphic rocks.

Sedimentary rocks:
Sedimentary rocks are formed at surface of the Earth by the hydrologic system. Their origin involves weathering of preexisting rocks, transportation of the materials away from the original site, and deposition of the eroded materials in the sea or in some other sedimentary environments.

Two main types of sedimentary rocks are recognized: a) clastic rocks consisting of rock and mineral fragments, and (b) chemical rocks and organic rocks, consisting of chemical precipitates or organic material (see the display by the window).

Stratification is the most significant sedimentary structure. It results from changes in erosion, transportation and deposition of sediments during the time the rock is being formed. Other important structures include, cross-bedding, graded bedding, ripple marks, and mud-cracks.

Sedimentary processes result in sedimentary differentiation, in which material is sorted, segregated, and concentrated according to grain size and composition.

The major sedimentary environments are (a) fluvial, (b) alluvial-fan, (c) eolian, (d) glacial, (e) delta, (f) shoreline, (g) organic-reef, (h) shallow-marine, and (i) deep-marine systems.

After you studied the three types of rocks take the "Rock Test 1, 2, 3, 4, and 5" on Moodle.