1 ES202 Lab 2 - Overview of Minerals, Rocks, and Plate Tectonics (Lab2_ver5.doc – Jan. 2012) Part 1 - Mineral Properties A ES202 lab mineral set is assembled in a tray at the back of the room. The tray consists of a number of mineral specimens that are numbered on the bottom of individual boxes. Each box contains several samples of each specimen, giving multiple students access to a given specimen at a given instant. This exercise is keyed to the 9th Edition of the AGI Geology Lab Manual. Familiarize yourself with the specimen numbers and look at the variety of specimens that you see. Complete the tasks below. Place answers in the space provided. 1-1. Mineral Cleavage and Fracture (p. 66-68 of lab manual) Some minerals display a characteristic cleavage pattern when they are broken into pieces. The type of cleavage is dependent upon the way in which atoms are organized in the crystal structure of the mineral, thus providing a diagnostic property that can be used to identify the mineral. A. Specimen 12 is a dark, platy-looking mineral that has a very well-defined cleavage pattern. _____________ How many "breaking planes" or "cleavage directions" do you observe for specimen 12? (p. 66) _____________ What other specimen (answer by specimen number) is similar in appearance to 12 with respect to number of cleavage directions? _____________ What is the main physical difference that you see between specimen 1 and no. 12 above? B. Specimen 4 is a translucent mineral (it passes light through it) that has a common usage in everyday life. _____________ How many different "breaking planes" or "cleavage directions" do you observe in specimen 4? (p. 66) _____________ What is the angle of intersection between the "breaking planes" or "cleavage planes" of this mineral (less than 90 degrees, 90 degrees, or more than 90 degrees)? _____________ Touch specimen 4 to your tongue, what is the characteristic taste of this mineral? C. Refer to specimen 8 and answer the questions below _____________ How many different "breaking planes" or "cleavage directions" do you observe in specimen 8? (p. 66 & 68) _____________ What is the angle of intersection between the "breaking planes" or "cleavage planes" of this mineral (less than 90 degrees, 90 degrees, or more than 90 degrees)? _____________ Place a small drop of dilute hydrochloric acid (in the small dropper bottles) on specimen 8, what do you observe? Wipe the acid from the sample with a paper towel when you are finished. (see page 69, Fig. 3.17) _____________ What happens when you place a small drop of HCl on specimen 3? Wipe the acid from the sample with a paper towel when you are finished.2 D. Refer to specimen 3 and answer the questions below. _____________ How would you best describe the "breaking characteristics" of specimen 3 (choose one): breaks into well-defined cleavage planes (list the no. of directions if you think this is correct), OR breaks or "fractures" like glass with no well-defined cleavage planes (better known as conchoidal fracture). _____________ Can you take a guess at what the name of this common silicate mineral is? 1-2. Mineral Luster and Light Transmission (p. 61 of lab manual) The luster or appearance of reflected light from a mineral is another diagnostic property that is used to identify minerals. Two luster types that are relatively easy to recognize are (1) metallic (shines like metal), and (2) non-metallic (does not shine like metal... for example glassy or dull). Other descriptive terms for luster include: (a) vitreous – shines like glass, (b) waxy – looks like candle wax, or (c) earthy or “dull”. The ability of a mineral to transmit light through it is also important. Some minerals allow light to pass through them, while others do not. Some options for light transmission characteristics include: (1) opaque (does not transmit light), (2) transparent (perfectly clear, like glass), and (3) translucent (allows some light to pass through, but not images). Refer to the appropriate mineral samples and answer the questions below. A. Specimen 11. _____________ Is this mineral opaque, transparent or translucent? _____________ Is the luster metallic or non-metallic? B. Specimen 2. _____________ Is this mineral opaque, transparent or translucent? _____________ Is the luster metallic or non-metallic? C. Specimen 3. _____________ Is this mineral opaque, transparent or translucent? _____________ Is the luster metallic or non-metallic? D. Specimen 15. _____________ Is this mineral opaque, transparent or translucent? _____________ Is the luster metallic or non-metallic? Question to think about and answer (and talk to the instructor about if you need to): What do you think is the primary factor that controls the physical appearance of a given mineral? That is, why are different types of minerals, well, different from one another?3 1-3. Mineral Color (p. 59 of lab manual) The color of a mineral may POSSIBLY be a diagnostic criteria to aid in identifying the specimen. Color is a function of the photo-atomic reaction of light energy with the atoms composing the substance. When all components of the visible spectrum of light are combined together, we refer to this as "white light". When select wavelengths of light are absorbed by atoms, and others are reflected, then "white light" is separated into it's component spectrum (i.e. colors of the rainbow ROY G BIV... you know). So the color of a mineral (or any substance for that matter) represents the select wavelengths of light that are reflected back to our eyes. For example a "green" color suggests that all other wavelengths are absorbed at the atomic level, but only the green part of the spectrum is reflected to our eyes. In sum, mineral color is variable, depending on the specific atoms and elements that comprise the specimen (for example, iron tends to give a red coloration, copper a bluish-green, iron-magnesium a black, etc.). Refer to the appropriate mineral samples and answer the questions below. Specimen 3 _____________ How many different colors of specimen 3 are evident in the sample box? List them. _____________ _____________ _____________ Mineral specimens can be separated into general composition categories by observing whether their color is "light" (e.g. pink, white, clear) or "dark" (black, dark gray, dark greenish-gray). Fill in the table below for the