Geology 106 LAB: Mineral Physical Properties and Identification

 

Purpose

A mineral is a “naturally occurring inorganic solid element or compound with a particular chemical composition or range of compositions and a characteristic internal structure.” (Stanley & Luczaj, 2015) The lab has a total of twenty samples that needs to be identified through the use of physical properties. The purpose of this assignment is to become familiar with the physical properties of minerals and how they are used in their identification. These descriptions of the samples fall in categories such as their cleavage, color, crystal form, fracture, hardness, luster, magnetism, reaction to hydrochloric acid (HCI), specific gravity, streak, taste, and other properties.

Procedure

  1. Identify the physical properties that are present through a series of tests and observations
  2. Identify the mineral

Data Collection

Data Processing

 

Summary

To identify minerals, physical properties are used in order to create a description that helps identify what type of mineral it is. Minerals are categorized with their cleavage, color, crystal form, fracture, hardness, luster, magnetism, reaction to HCI, specific gravity, streak, taste, and other properties. Some physical characteristics of the samples are more helpful than others to identify what the sample may be. However, some tests are not needed in order to conclude for a result. Using all of these different properties throughout the identification process makes it easier to figure out and narrow down the name of the sample.

One of the most useful physical properties is the hardness of the mineral, which is the “resistance to scratching or abrasion” (Harwood, 2011). This is conducted by scratching the unknown mineral with a mineral with a known hardness to determine which one is harder. This characteristic is extremely helpful with the majority of samples of the lab. Just like hardness, cleavage also helps with the process of identifying the minerals. Cleavage is the “breakage of a mineral along planes of weakness in the crystal structure” (Harwood 2011). To determine the number of cleavage direction the sample may have, it was necessary to find areas where the sample is broken to see where the light reflects from planar surfaces. The same test also concludes the type of breakage it is, which is known as fracture. The breakage can either be irregular or conchoidal, when it looks like broken glass. The color of the sample helps identify the mineral as well. However, some minerals can be described with a variety of colors that can make it difficult to pinpoint what mineral it is at times. Even though most colors are universal, there can still be some debate on what color the sample is with all the different mixtures of shades presented. Although this can be true here and there, the color does give an advantage on some samples in this lab.

The remaining physical properties use to examine the samples are not as effective as they could be for this lab. For example, the categories luster, magnetism, reaction to hydrochloric acid (HCI), and taste are only able to name a sample to a particular mineral. Luster, “the character of light reflection of the mineral” (Harwood, 2011) to observe whether or not the material has a metallic appearance, only help define Sample 16 as Galena. Magnetism, “the electromagnetic force generated by an object or electrical field” (Harwood, 2011), is able to identify Sample 7 as Magnetite by using a magnet to see if the sample is attracted. The only sample that reacts to hydrochloric acid was sample 17, which helps identify the sample as the mineral Calcite. A reaction to hydrochloric acid is the “chemical interaction of hydrochloric acid and calcium carbonate (CaCO3)” (Hardwood, 2011), which is indicated through a reaction from a drop of HCI. In addition, the taste of the sample or the “nerve ending reaction in the tongue to different chemicals” (website) figures out Sample 10 as Halite with its saltiness.

The most difficult physical property to describe is the crystal form, which is the “geometric shape of a crystal or mineral” (Hardwood, 2011). Since the majority of the minerals are very difficult to pinpoint what shape it naturally has, this category is not that helpful as it could have been. A lot of samples did not have their form available as a choice in the lab, meaning that it is not beneficial in knowing what form the sample took. However, this is not true for all the samples of the lab. Some examples are samples 5, 8, 11, 19 that had a specific description of their crystal form to help identify that they are Corundum, Apatite, Muscovite, and Biotite. There are also physical properties that are not available to test or observe, such as specific gravity, fluorescence, and radioactivity. Even with not being able to experiment with these characteristics, it would not be helpful in any way since the descriptions of the minerals did not have anything related with such physical properties.

The mineral identification table where all the minerals are characterized could have been more descriptive in order to help identify what mineral the sample is and shorten the time it takes as well. The majority of descriptions for the minerals did not have every single physical property defined specifically for it, making it difficult to narrow down the possibilities. Even with all of the different types of characteristics that help evaluate what the mineral may be, not all was mentioned in the description. Some descriptions are very broad and nonspecific, so the only way to figure out the mineral is through process of elimination and when that did not work it resulted to guess and check. This leads to misidentification of a sample or result in a longer process of naming what mineral it is.

Overall, having all of these different descriptions of the physical properties of the sample allows the cancelation of the majority of minerals it could have been mistaken for. Some characteristics helps establish what mineral it is more than others. It does not hurt to have more physical properties described, but not all do help with the identification. What is really needed to help certify what mineral the sample is, is to retain a major feature that gives a direction of what it may be. There are definitely key features of a mineral that helps define it the most, but having extra data and information can always improve the process.

 

 

References

Gore, P. J. (2014). Historical Geology Lab Manual. Hoboken, NJ: John Wiley & Sons, Inc.

Harwood, R. (2011). EARTH SCIENCE LAB Mineral Physical Properties and Identification.

Retrieved May 28, 2017, from

http://facweb.bhc.edu/academics/science/harwoodr/geol101/labs/minerals/index.htm

Stanley, S. M., & Luczaj, J. A. (2015). Earth system history (Fourth ed.). New York, NY:

Freeman.

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