Mineral Identification Lab

Name _______________________________________________ Date _________________ Mineral Identification Lab The common minerals in this collection all have distinguishing characteristics which identify them. Geologists often use their five senses and simple tests to determine what a mineral is. Purpose: You will be trying to identify 15 mineral samples, which include the minerals in the table below along with their characteristics. Procedure: 1) Read the information provided in this handout on pages 2-5 about properties and characteristics of minerals. 2) Watch the YouTube video linked below to see several tests on each mineral to measure key properties that will allow you to identify the mineral. As you watch the video, fill in the table on page 6 with the information provided. Make note of other helpful properties used to identify each mineral. https://youtu.be/st2yhTuUCxg 3) When you have the properties and characteristics of all 15 minerals, name each mineral based on the properties in the table below. Mineral Name Calcite Color(s) white, yellow, brown, blue Luster vitreous to earthy Streak Hardness white 3 Other Properties often fluorescent and has many colors cleavage angle is just under 90 degrees forms cubic crystals and often fluoresces Feldspar var. Microcline white, red, green vitreous white 6 Fluorite green, yellow, purple vitreous white 4 Graphite black black 1-2 white 2 can be scratched by a fingernail silky white 2 fibrous gypsum colorless transparent white 2 bladed gypsum colorless, white, pink transparent dull to metallic metallic white dark red black 2.5 5.5-6.5 Gypsum var. Alabaster Gypsum var. Satin Spar Gypsum var. Selenite Halite white, gray, yellow white, gray metallic to dull pearly to earthy greasy feel Hematite red, brown, black Magnetite iron-black Mica var. Biotite green, brown, black splendent none 2.5-3 Mica var. Muscovite colorless, yellow, brown vitreous to pearly none 2-2.5 Pyrite pale brass yellow metallic brown 6-6.5 Quartz var. Milky colorless to white none 7 Talc white, green, gray vitreous pearly to greasy salty taste becomes magnetic upon heating magnetic thin sheets are elastic (tenacity) thin sheets are elastic (tenacity) is brittle and has conchoidal fracture conchoidal fracture white 1 greasy feel, sectile (tenacity) 6 1 Name _______________________________________________ Date _________________ A mineral is a naturally occurring, inorganic substance that has an orderly internal arrangement of atoms and a definite chemical composition that may vary within certain limits. Each mineral possesses specific physical properties, many of which are nearly constant for a particular mineral species. Therefore, the first step in identifying an unknown mineral specimen is to recognize the relevant physical properties. Minerals also possess chemical properties, most of which require sophisticated investigations to define, but may aid in their identification. Some simple tests of chemical properties, such as effervescence of calcite in dilute HCl, can be diagnostic. Hardness: Hardness is the resistance that a smooth surface of a mineral offers to abrasion. Like many other physical properties of minerals, hardness is dependent upon crystal structure. The hardness is expressed in terms of a relative scale from 1 to 10, each number being represented by a special mineral. This scale, known as Mohs' scale of hardness, is as follows: Mohs Scale 1 Talc 2 Gypsum 3 Calcite 4 Fluorite 5 Apatite 6 Orthoclase 7 Quartz 8 Topaz 9 Corundum 10 Diamond Common Item 2.5 - thumbnail 3 - penny 5 - nail 5.5 - glass 7 - streak plate In determining the hardness of a mineral it is necessary to see which common substances (above) the mineral will scratch and which ones it will not. Some of the common substances above will be provided for you, and the gaps can be filled in by minerals in the study set after they are identified. The following should be observed when testing the hardness of a mineral: 1) When testing the hardness of one mineral against another, the softer mineral may leave a mark on the harder one which can be mistaken for a scratch. However, this mark is not permanent and can be easily rubbed off, while a true scratch will be permanent. For example, when chalk is rubbed across a blackboard, a mark is left on the board. This mark, however, is chalk that has rubbed off on the board, rather than a scratch on the board, and can be easily rubbed away. 2 Name _______________________________________________ Date _________________ 2) When testing the hardness of a mineral against that of a nail, try scratching the mineral with the pointed end of the nail. If no scratch is made, find a sharp edge on the specimen and rotate the nail against it. A mineral having a hardness of 7 will cut the nail easily. One with hardness 6 will cut slightly if sufficient pressure is applied, although the mineral edge may be somewhat crushed. (One should be aware that the hardness of nails may vary over a range of types). Color: Color is one of the most obvious physical properties, but because it can be highly variable, it is one of the least valuable diagnostic properties. Trace quantities of certain elements (e.g., iron, manganese, etc.) in the crystal can cause wide variations in color among examples of the same mineral species. Quartz, for example, has no inherent color of its own, but varies according to the occurrence of these impurities within its crystal lattice. Color is relatively constant for most metallic minerals. A good example is pyrite, a mineral that is always brassy yellow. Luster: Luster refers to the way in which a fresh surface of a mineral reflects light. Many nonmetallic minerals have a glassy luster. Metallic luster is characteristic of metals and sulfide minerals such as pyrite (iron sulfide) and galena (lead sulfide). Weathering of the surface may obscure the true luster. Some minerals truly have a dull "luster", even on fresh surfaces. Cleavage: Cleavage is the tendency shown by many minerals to break along certain welldefined planes that represent planes of weakness in the bonds that hold the atoms together in the crystalline structure. A planar surface so produced is characteristically flat and reflects light to differing degrees depending on the degree of perfection of the cleavage; see the figures for examples of cleavage types. The flat surface is called the cleavage plane, and the orientation of the plane is called the cleavage direction. Some minerals have only one such cleavage direction; the micas are excellent examples. Notice that although the micas have only one cleavage direction, this cleavage direction is represented by two parallel planes, one on top of the specimen, the other on the bottom. The feldspars have two directions of cleavage. A mineral may have 2, 3, 4 or more directions of cleavage, and there may not be a dominant direction; that is, the mineral might break with equal ease along all cleavage directions. This can result in the formation of a stair-step surface that may at first appear to be an irregular fracture. Galena, a mineral that has three directions of cleavage in cubic orientation, and because none of these directions of cleavage is dominant, a stair-step pattern results. Each of these "steps" represents a side of a cube. If such a specimen is rotated in the light the small parallel cleavage surfaces will reflect light in the same manner as will the large smooth cleavage surface. An uneven fracture will not concentrate light in any particular direction, and therefore will not appear shiny. In minerals with two or more directions of cleavage, the angles at which the different cleavage directions intersect are important and diagnostic. Exact measurements of these cleavage angles are seldom necessary, as careful estimation is usually sufficient for determination. 3 Name _______________________________________________ Date _________________ Fracture: In some minerals the internal bonding is so uniform in strength that there are no planes of weakness in the crystal structure. Such minerals do not have cleavage, but instead break or fracture in an irregular random manner. There are two important types of fracture: CONCHOIDAL - smooth, curved fracture (like glass). UNEVEN - rough and irregular surfaces. Other diagnostic properties: taste, feel, magnetic character, etc. Vocabulary Terms Cleavage: (klE'vij), —n. The tendency of a mineral to split along specific planes, determined by the crystal structure. Conchoidal: (kong-koid'l), —adj. a shell-like or spiral fracture produced on certain minerals. Fibrous: (fī-brəs), —adj. capable of being separated into fibers Fracture: (frak'chur), —n. the appearance of a broken surface Hardness: (härd'nis), —n. Resistance of a mineral to scratching, determined by the Mohs Scale. Luster: (lus'tur), —n. The manner in which light reflects from the surface of a mineral, described by its quality and intensity. Metallic: (mu-tal'ik), —adj. a luster resembling the surface of a metal. Mohs scale: (mOz skAl), —n The ten-point scale of mineral hardness, based on the minerals talc (1), gypsum (2), calcite (3), fluorite (4), apatite (5), orthoclase (6), quartz (7), topaz (8), corundum (9), and diamond (10) in increasing order of hardness. Sectile: (sek-təl) —adj. capable of being severed by a knife with a smooth cut Splendent: (splen-dənt), —adj. a shiny, glossy luster Streak: (strEk), —n. The color of a mineral in its powdered form, usually obtained by rubbing the mineral against an unglazed porcelain tile to see the mark it makes. A mineral harder than the tile must be pulverized by crushing. Vitreous: (vi'trE-us), —adj. a luster resembling glass, as in transparency, glossiness, etc. 4 Name _______________________________________________ Date _________________ 5 Name _______________________________________________ Date _________________ Mineral # Color(s) Streak Magnetic (Yes or No) Is it scratched by: Fingernail Penny Nail (Yes or No) Hardness (1-10) Luster Mineral Name 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 6