GOL 105: Mineral Identification Lab

Transcription

1 Northern Virginia Community College Alexandria, Virginia Dr. Victor P. Zabielski GOL 105: Mineral Identification Lab Objective: Minerals are the basic building blocks of all rocks. The identification of minerals is one of the most basic skills in geology. Although there are over 4000 different minerals, a working knowledge of of them will allow you to identify most rocks by their composition. The objective of this lab is to introduce you to the diagnostic properties of minerals and acquaint you with several of the most common minerals that you will encounter in most rock types. Part I: Diagnostic Properties Provide brief descriptions for each of the following diagnostic properties of minerals. For each property, give an expected range of values (for example, transparency can range from transparent to translucent to opaque). You will use these properties to help you identify the mineral specimens in this lab. Definitions for each of these properties can be found in your Laboratory Manual in Physical Geology (Laboratory 3, p. 37) and in your textbook Essentials of Geology, (Chapter 3, section 3.4, p. 87). Habit (or Shape) Cleavage Fracture

2 Hardness Specific Gravity Color Streak Clarity / Transparency (light penetration) Luster (light reflection) Accesory properties (texture, magnetism, etc..)

3 Part II: Mineral Identification This exercise is meant to get you to learn how to identify minerals using the properties that you described in part I of this lab. First, list the properties of each of the minerals in the accompanying Mineral Identification Charts provided. Some properties will be more easily determined than others. Second, use the flow charts at the end of this lab to help you identify each of the minerals. The flow charts are designed to allow you to use the most basic and simplest properties to first identify the mineral (color and cleavage) and then to further narrow down the minerals identity using other less obvious properties (hardness, streak, specific gravity, etc). Finally, not all properties of every mineral are equally useful. Generally you will be able to identify a mineral by using only two or three primary properties. These will differ for each mineral. For instance, although pyrite has a hardness of 6 6.5, this is not generally a primary property. You will likely be able to identify pyrite by the fact that it is gold colored and has cubic cleavage (3 cleavage planes), thus the color (gold) and cleavage (cubic) will be the primary properties for pyrite. Determine which properties are most valuable in helping you identify each mineral and enter these properties in the last column of your chart. This will be valuable for your study guide. I will distribute an answer key later in the lab, but first try to describe the samples on your own. Figures in your lab manual will also help you determine the identity of the minerals (pages 52 54). Your manual also contains a mineral database (Figure 3.28, pp ) and additional data sheets for your use (pp ) GREAT RESOURCE ALERT! You can also refer to the website for pictures and descriptions of the minerals and rocks. You can find a link to this website on my homepage.

4 Sample Number Color / Streak Hardness Mineral Identification Chart Number of Cleavage Planes Shape Other Properties (luster, transparency) Mineral Name Primary Properties

5 Sample Number Color / Streak Hardness Mineral Identification Chart Number of Cleavage Planes Shape Other Properties (luster, transparency) Mineral Name Primary Properties

6 Sample Number Color / Streak Hardness Mineral Identification Chart Number of Cleavage Planes Shape Other Properties (luster, transparency) Mineral Name Primary Properties

7 Sample Number Color / Streak Hardness Mineral Identification Chart Number of Cleavage Planes Shape Other Properties (luster, transparency) Mineral Name Primary Properties

8 Mineral Identification Flow Charts Color Cleavage Hardness Distinctive properties gold color, perfect cubic cleavage Mineral Pyrite High specific gravity, silvery grey Galena Metallic Cleavage good to excellent dark silvery grey to black, 1 plane of cleavage, very soft, will leave a black mark when scratched on paper gold color, perfect cubic cleavage dark grey to black, will be attracted to a magnet Graphite Pyrite Magnetite Cleavage poor or absent Brass-yellow color, dark grey streak dark grey to silver, red streak dark grey to black, will be attracted to a magnet Chalcopyrite Hematite Magnetite

9 Color Cleavage Hardness Distinctive properties 2 planes of cleavage, striations on surface, slightly translucent 2 planes of cleavage, opaque Mineral Plagioclase feldpsar Potassium Feldspar Fizzes w/ HCl when powdered 3 planes of cleavage, fizes readily in HCL Dolomite Calcite often colorful (clear, purple, green red, yellow, blue), cubic or octahedral, translucent Flourite Light Colored Cleavage good to excellent perfect cubic cleavage and habit, usually transparent, tastes salty powdery texture, very soft, basal cleavage may not be apparent clear and transparent, peels into thin sheets opaque, generally, white, grey or green, greasy or soapy texture, can scratch with fingernail clear, white, grey, yellow, can scratch with fingernail Halite Kaolinite Muscovite Talc Gypsum green color conchoidal fracture, rose colored, transparent to translucent opaque, can be namy colors, waxy luster, concoidal fracture Olivine Rose Quartz Chalcedony Cleavage poor or absent transparent to opaque, usually white to grey, conchoidal fracture Quartz powdery texture, very soft, perfect basal cleavage may not be apparent Kaolinite powdery texture, rustybrown to yellow color, dark yellow streak Limonite

10 Color Cleavage Hardness Distinctive properties 2 planes of cleavage, striations on surface Mineral Plagioclase feldpsar Fizzes w/ HCl when powdered 2 planes of cleavage at a 60 to 120 degree angle, black Dolomite Amphibole Cleavage good to excellent Cleaves into thin sheets Biotite often colorful (clear, purple, green red, yellow, blue), cubic or octahedral, translucent Flourite Dark Colored 2 planes of cleavage at nearly right angles, greenish-black dodecahedral habit (12-sides), deep red dark grey to black, will be attracted to a magnet Pyroxene Garnet Magnetite green color Olivine opaque, can be namy colors, waxy luster Chalcedony Cleavage poor or absent dark grey to silver, red streak Hematite powdery texture, rusty-brown to yellow color, dark yellow streak dark grey to black, will be attracted to a magnet Limonite Magnetite