Name: ______

EPS 50 Lab 01: Properties of Minerals and Rocks Grotzinger and Jordan, Chapter 3

Due: Monday 1 pm

Introduction: Geologists study rocks and minerals because these materials provide information about the formation and evolution of our planet, including Earth’s composition, age, resources, and dominant processes. Because rocks and minerals persist for thousands, millions, or even billions of years, they provide a record of Earth’s history. This record is difficult to interpret, but with careful observations and analyses, we can get a glimpse into deep time. The first step is being able to identify these materials.

Objective: In this lab you will learn to distinguish amongst minerals based on a few qualitative diagnostic tests. Along the way you will begin to recognize some of Earth's basic minerals and their general chemistries. You will also learn to determine major rock types. Be sure to keep samples in their proper boxes!

Answers: Please answer the numbered questions on the separate answer sheet handed out during lab. Only the answer sheet will be graded. Explanations should be concise - a few sentences or less. All answers should be your own, but we encourage you to discuss and check your answers with a few other students as you move through the exercises, unless specified otherwise.

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Basic Observations 1) Look at the large piece of granite in Tray 1 and write down at least five observations about this rock. Draw a sketch showing the details of these features. (3 pts).

2) Note the smaller hand samples in Tray 1. These samples are examples of the diversity of minerals within granites. List at least five criteria you can use to distinguish these samples from one another in terms of the minerals present and their relative abundances. (3 pts).

Part 1: Minerals and Mineral Properties The different substances within the piece of granite you just studied are called minerals. Geologists define a mineral as a naturally occurring, inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and other identifying physical properties. In simpler terms, minerals are formed from the specific bonding of different combinations of atoms in a solid form. The atoms can be of the same element, or of many different ones. To keep track of the type and amount of different elements, each mineral is given a specific chemical formula (e.g. FeS2 or CaCO3). A rock is an aggregate of minerals.

Thousands of different minerals have been identified and cataloged by mineralogists, but the vast majority of rock-forming minerals belong to one of these six groups (you should know these!): Feldspar Quartz Mica Pyroxene Amphibole Calcite

Other common minerals include oxides (e.g. hematite: Fe2O3), salts (e.g. halite: NaCl), and sulfides

(e.g. pyrite: FeS2). Each mineral has different physical and chemical properties. Physical properties you will use to identify the minerals include color, , hardness, luster, density, habit, , magnetism, fluorescence, and reaction to chemicals. Refer to Appendix 3 in the back of your book or any reference book for properties of common minerals.

Mineral Color and Streak The color we perceive from minerals results from light reflected off the surface of the crystal; it is determined by elements or defects in the . When reporting mineral or rock colors in this lab (and in your field work), use objective descriptive words. Avoid subjective adjectives like 'cream', 'buff', or 'rosy'. Instead, use conventional terms such as 'very light yellow', 'light brown', and 'pale orange-pink'. While color can be a useful tool for identifying some minerals, it is not generally diagnostic. Quartz is made of silica and oxygen (SiO2) often packed into a six-sided prism shape that ends in pyramids. If only two elements (Si and O) are present, the mineral quartz appears transparent. Yet, if a tiny amount of an impurity is present in the crystal, the result is colored quartz.

3) Tray 2 contains several different quartz samples. Write down the different colors of quartz you observe using objective descriptive terms. (4 pts).

Another test performed in conjunction with surface color is the streak test. A streak is made by firmly drawing the mineral sample across an unglazed porcelain tile called a streak plate. The resulting mark of powdered mineral is often an excellent diagnostic tool. If a mineral is harder than the porcelain tile, it will not leave a streak (the streak is said to be 'colorless'). Some streaks will appear white and are best seen on a black or dark colored porcelain tile.

4) Using Tray 3 describe the colors of the two varieties of hematite, limonite, magnetite, and pyrite. Write in the chemical formula and describe the streak color for each. (5 pts).

Mineral Hardness The hardness of a mineral is a measure of its resistance to scratching and is related to the interatomic bond strength. The stronger the bond between the atoms, the harder the mineral. Friedrich Mohs, a 19th century German mineralogist, devised a relative scale on which minerals are ranked by hardness. Talc and graphite are the softest minerals with a hardness of 1; diamond is the hardest mineral at 10. The Mohs hardness scale is shown below, along with some common items that can be used for reference. Examine a mineral hardness kit and briefly look up the descriptions of the Mohs reference minerals so you can become familiar with them.

Care should be exercised in determining the relative hardness of two minerals. Sometimes when one mineral is softer than another mineral, parts of the first may rub off on the second and leave a mark that may be mistaken for a scratch. Such a mark can be easily removed with a damp finger whereas a true scratch is permanent. It is always advisable to confirm the result of a scratch test by reversing the procedure: see whether the second mineral will scratch the first.

5) Test the hardness of the minerals found in Tray 4. Also note the chemical formula and the mineral color. (4 pts).

6) While diamond and graphite are chemically identical (they both consist of pure carbon), they occur at the opposite ends of the hardness scale. Why is this? (2 pts).

Mineral Luster Luster refers to the way light is reflected from the surface of a mineral. Luster is divided into two main groups: metallic and nonmetallic. The luster of pyrite is a typical metallic luster. Nonmetallic luster can be further described by such terms listed below. Luster description is often subjective, and therefore not very diagnostic. To help understand luster, examine the minerals in Tray 5.

Mineral Luster Terms ~ Metallic: strong, mirror-like reflections produced by opaque substances ~ Non-metallic - Vitreous: producing a bright, hard reflection, as in glass - Resinous: characteristic of resins, as in amber - Waxy: reflecting a fuzzy, diffuse light - Pearly: iridescence similar to the appearance of a pearl - Silky: sheen of fibrous materials such as silk - Earthy: dull and powdery, as in a clump of dirt

7) Describe the luster, chemical formula and color of the minerals from Tray 5: galena, limonite, quartz, biotite, and two samples of gypsum. (6 pts).

8) Explain why you think the luster is different for the gypsum A and gypsum B samples. (2 pts).

Mineral Density The specific gravity of a mineral is the ratio of its weight to the weight of an equal volume of pure water at 4˚C, which has a density of 1 g/cm3. Common rock forming minerals have specific gravities in the range of 2.6 - 2.8, but heavier minerals can have specific gravities up to 8. Specific gravity can be measured very precisely in the laboratory but may also be roughly estimated simply by holding the specimen in hand.

9) Classify the samples in Tray 6 as 'heavy', 'average' or 'light' by weighing each specimen in your hand. Record the chemical formula for each. (4 pts).

10) Make a guess as to why the heavy minerals are so heavy. Hint: see the periodic table. (2 pts).

Crystal Shape or Habit The form a crystal takes is a function of its chemical bonding pattern. As a mineral grows, it builds up a 3-dimensional array of the elements in its chemical formula in a crystal form. With no barriers to its external growth, a mineral will form a perfect crystal. A perfect crystal is rare, however, and more commonly, adjacent crystals interfere with each other’s boundaries during later growth stages. Also, internally, the patterns formed may have planes of weakness. In spite of this, the fundamental form of a crystal, called the , is generally distinguishable, and is a useful diagnostic tool.

Crystals of the same mineral will always form the same angles between the same crystal faces. These interfacial angles are a good diagnostic tool, and can be precisely measured using a contact goniometer. Simple minerals, such as halite (NaCl) often form simple crystals. More complex minerals with complicated chemical bonding can form more interesting shapes.

Crystal habits

Massive Indiscernible masses of crystals usually too fine to see. Lazurite forms massive examples.

Micaceous Flaky to platy crystals compacted together in sparkling masses. Mica group.

Bladed Elongated and flattened like a blade of grass. More elongated than platy and thinner than tabular. Kyanite forms crystals that are a good example of bladed crystals.

Equant Any three perpendicular axes through the crystal are more or less equal. Can be used to describe rounded as well as angular crystals. Fluorite forms crystals that are a good example of equant crystals.

Prismatic One of the most common of crystal habits. Prismatic crystals are "pencil- like", elongated crystals that are thicker than needles (see acicular). Indicolite (a variety of elbaite) forms good examples of prismatic crystals.

Tabular Book-like (tablets) that are thicker than platy but not as elongated as bladed. Wulfenite forms crystals that are a good example of tabular crystals.

Fibrous Thinner than acicular crystals in either individual crystals or in a tight compact almost cloth-like mass. Okenite forms crystals that are a good example of the fibrous habit.

11) Describe the crystal habit of the five samples in Tray 7. (5 pts).

Mineral Cleavage Cleavage refers to how a mineral breaks along weak planes in the internal crystal structure. Some minerals, such as quartz and olivine, do not have cleavage. Instead, they have a special type of breakage called conchoidal . Conchoidal fracture produces curved breakage surfaces, such as would be seen on arrowheads or chipped glass. A mineral can either fracture or cleave. Minerals that cleave may have up to four directions of cleavage, and the resultant angle between the cleanly broken faces is diagnostic of the particular mineral. The best way to observe cleavage is to hold the sample between you and a light source (windows are best) to get a reflection off the surface. A cleavage surface is smooth and will reflect light.

The quality of the cleavage surface is sometimes diagnostic. Cleavage can be perfect (smooth and shiny), good (shiny but not perfectly smooth), or poor (with stepped or terraced faces). You can find the number and types of cleavage planes a certain mineral has in mineral identification handbooks or websites such as www.mindata.org.

It is easy to confuse crystal faces with cleavage faces. Crystal faces are the outer walls of a perfect or partially perfect crystal and may separate one crystal from the next.. In contrast cleavage faces are exposed when a crystal breaks along weak planes in the crystal structure. Often cleavage faces are cleaner than crystal faces. Keep the two types of surfaces distinct in your descriptions.

Minerals belonging to the sheet silicate class have very weak bonds between separate silicate sheets, resulting in the characteristic cleavage of micas into thin sheets. Because they have no other direction along which they break, micas have one direction of cleavage. Halite, however, breaks into neat cubes with 90° angles between the faces, with parallel faces on the top and bottom, on the left and right sides, and on the front and back. Therefore halite has three perfect cleavages.

12) Identify the number and angles of cleavage planes for the samples in Tray 8. Estimate the angles between the cleavages, and the quality of the cleavage. If the sample has no cleavages, report 'fracture' for the number of cleavages and "N/A" for the quality and angle. Make labeled sketches of 3 contrasting samples. (10 pts).

Chemical Reactivity Some minerals can be identified by a chemical reaction with other materials. An example is the reaction of calcite (a carbonate mineral) with dilute hydrochloric acid (HCl): the calcite dissolves and fizzes, releasing CO2 gas. When calcite occurs in a rock in amounts too small to test for hardness or cleavage, drops of acid allow you to quickly distinguish it from quartz. Other examples of useful chemical reactions include halite and other salts dissolving in water.

Determine which of the samples in Tray 9 (sample #1 or sample #2) is chemically reactive to a dilute acid. Put one or two drops of 5% HCl onto a sample and watch to see what happens. Then answer the questions below. When you are finished, rinse the sample with water and dry it off. Also rinse off your hands.

13) Calcite effervesces in the presence of HCl. Which sample is calcite, which is quartz? (1 pt).

14) Halite dissolves in water. Which sample is halite, which is gypsum? (1 pt).

15) There are many other diagnostic properties of minerals. Name and describe at least two diagnostic properties that we have not yet explored. For each property, list a characteristic mineral that might display that property. (4 pts).

16) Identifying Minerals (20 pts) Identify the ten unknown minerals in Tray 10 on the chart provided on the answer sheet. Start by examining the sample and determining which properties will be most useful in determining the mineral identity. There is no need to fill in all of the spaces for all of the minerals! Only use those mineral properties that are appropriate for the individual sample. When you are DONE, compare your results with 2-3 other students. Write your partners’ names at the bottom of the table.

Part 2: Rocks and Rock Properties

A rock is a naturally occurring material consisting of minerals or fragments of other rocks. The chemistry (or composition) and texture (size and shape of the component pieces) of a rock depends on the process by which it was formed. Processes that form rocks occur in particular places on the surface of the earth. For example, reef rocks form in tropical waters, and volcanic rocks form in places where heat and magma are generated.

Rocks can be classified into three main categories (igneous, sedimentary and metamorphic) depending on the conditions of their formation. Rocks are the building blocks of the Earth's crust. The Earth's continental crust is dominated by granite, and the oceanic crust is dominated by basalt. Both of these rocks are igneous. By studying the composition and texture of a rock along with its context (provenance), we can begin to understand the original conditions of its formation.

Igneous, Sedimentary and Metamorphic rocks Igneous rocks are cooled from molten material called magma. As the magma cools it forms crystals. Depending on how quickly molten magma cools, crystals may be large or they may be microscopic in size. Igneous rocks that cool deep within the Earth are called plutonic or intrusive (e.g. granite). Intrusive igneous rocks cool more slowly and have larger crystals. Igneous rocks which cool on or near the surface of the Earth are referred to as volcanic or extrusive igneous rocks, and include a type of dark-colored lava called basalt which comprises most of the seafloor. Extrusive igneous rocks cool more quickly than intrusive rocks, leaving less time for crystal growth. Tray 11 contains both intrusive and extrusive igneous rock examples.

Sedimentary rocks form from the accumulation of eroded bits of pre-existing rocks. The bits come from rocks exposed at Earth’s surface, which are broken down by water and wind via a process called weathering. Loose, weathered material will travel down slope via wind, water or gravity as sediment and collect in a basin. The transport and deposition of sediment occurs at surface pressures and temperatures. The most common way in which loose sediment becomes rock (lithification) is through burial by other sediment: the weight of the overlying sediments compacts the whole sediment pile and, given enough time, causes the originally loose sand or clay particles to bind together and become a rock. Sedimentary rock can also be formed through precipitation of chemicals either directly from water (evaporites) or through biological means (limestone), which act to cement the formerly loose particles together. Sediment can also lithify by a combination of both compaction and chemical precipitation. Tray 12 contains sedimentary rock examples.

Metamorphic rocks have been subjected to extreme heat or pressure such that the chemistry and structure of the rock is altered from the starting material, or protolith. Often the size and shape of the component mineral crystals or grains are altered as well. Metamorphic rocks are formed in places in the Earth where pressures or temperatures are very high, (e.g., where tectonic plates collided, where magma bodies raise the temperature of surrounding rocks, and where rocks have been pushed into the mantle on a down-going tectonic plate). Tray 13 contains examples of metamorphic rocks.

Common Minerals of Major Rock Types Igneous Rocks Quartz, Feldspar, Mica, Pyroxene, Amphibole, Olivine Sedimentary Rocks Quartz, Feldspar, Clays, Calcite, Dolomite, Gypsum, Halite Metamorphic Rocks Quartz, Feldspar, Mica, Garnet, Pyroxene, Staurolite, Kyanite

Distinguishing Basic Rock Types Rock Type Diagnostic Features

Igneous Made up of intergrown or interlocking crystals. Do not (usually) have a preferred orientation of the mineral crystals.

Sedimentary Made up of distinct grains or rock fragments. Sedimentary rocks are frequently softer than igneous rocks, and will break around grains. Clay, sand, and shells are common sedimentary materials. Samples often show layering.

Metamorphic Most often made up of crystals that show a distinct fabric or preferred orientation of the mineral components called rock cleavage. Rock cleavage may look like layering, but is different in that it is formed by the orientation of crystals that have grown in place, not by grains that were carried in and deposited.

17) Distinguish between granites and sandstones in Tray 14 by determining which is made up of intergrown crystals and which is made up of distinct grains. Use the descriptive language you learned in Part 1 and in the table above. (6 pts).

18) Distinguish between a mudstone and a schist in Tray 15. Which is made up of undeformed grains and which has crystals lying in a preferred orientation? (6 pts).

19) Identifying Rocks Working independently, examine the rocks in Tray 16. Determine the rock type and list three diagnostic features you used to classify each one. (12 pts).