Rock Cycle - Minerals (4A)
 Lab 

   
OBJECTIVES:
  • Exploring the characteristics of minerals.
  • Distinguishing mineral attributes.
VOCABULARY:
  • color
  • density
  • feel
  • hardness
  • shape
  • texture
MATERIALS:

Students look at minerals and determine key characteristics.


crystals of feldspar

BACKGROUND:

A mineral is "a naturally occurring, inorganic element or compound with a definite chemical composition, a characteristic crystalline structure, and distinct chemical properties". Minerals have to be naturally created or else they are classified as man-made substances. Minerals are the building blocks of rocks.

Most minerals have key characteristics that help in their identification. Halite (table salt), which is composed of sodium (element #11) and chlorine (element #17) is a good example. The key characteristics of halite are its cubic crystal shape, lack of color (it is clear) and salty taste. Knowing these characteristics helps identify halite.

PROCEDURE:

In the lab, the students will work at stations to begin to distinguish the key characteristics of minerals. These include color, hardness, density, crystal shape, texture and cleavage.

  1. Prior to lab, cut the "Mineral Cards" for each station listing the questions that you want the students to answer. Place the cards in front of the minerals. If the card asks the students to perform a test, such as scratching the mineral with a nail, make sure that the correct materials are available.
      
  2. Using the Periodic Table Placemats, review the composition of each of the minerals in the lab. You can use the cards that accompany the specimens as a guide to composition. Direct the students to locate the elements on the periodic table as you tell them the "ingredients."
      
  3. After students have completed the lab, discuss the specific key characteristics of each mineral. Use the information below as a guide.

QUARTZ is a naturally clear mineral. It can occur in almost any color, however, if it contains traces of other elements. Its natural crystal shape is 6 sided. Quartz is very hard (7 on Mohs hardness scale). It cannot be scratched by a steel knife or nail. Quartz is the most common mineral on the surface of the Earth. It is found in nearly every geological environment and is a component of almost every rock type. Quartz is used to make glass, electrical components, optical lenses, and abrasives. It is also used as a gemstone, ornamental stone, and building material.

FLUORITE breaks into 8 sided polygons (dipyramidal shapes). It has a hardness of 4 on the Mohs scale. Fluorite is prized for its glassy luster and rich variety of colors, including purple, blue, green, yellow, colorless, brown, pink, black and reddish orange. Most fluorite from the United States is clear to purple in color. The word fluorite comes from its use as a flux in steel and aluminum processing. Fluorite is also used as a source of fluorine for hydrofluoric acid and fluorinated water.

PYRITE shows cubic crystal forms. It has a metallic luster, and a distinctive brassy-to gold color. Since it is composed partially of iron, is very dense. Because of its color, pyrite is the classic "fool's gold." Pyrite has been mined for its sulfur content for use in defense and chemical industries.

GYPSUM crystals are tabular in shape. Gypsum ranges from white to pink in color. It is very soft, and can be scratched by a fingernail. Gypsum is one of the more common minerals in sedimentary environments. It often forms in desert areas where evaporation rates are high, by precipitation from highly saline water. Gypsum’s uses include plaster, wall board, cement, fertilizer, paint filler, and ornamental stone.

CALCITE forms the rhombohedral and hexagonal prism shapes. It occurs in light shades of white, yellow, orange, blue, pink, red, brown, green, black, and gray. It may also be colorless. Calcite fizzes readily with HCl. It is soft (about 3 on the hardness scale) and is easily scratched with a knife. Calcite may be clear to yellow in color. When a clear calcite crystal is placed over an image or word, it appears doubled when viewed through the crystal. This is called double refraction.

MICA crystals occur in very thin sheets. This is an excellent example of a mineral with one cleavage; the sheets form along a plane of weak atomic structure in the mica crystals. Mica is used as a heat insulator. There are two common types of mica: a) biotite(black to brown color) and b) muscovite (clear, white, or silver in color). Mica is a common rock forming mineral; it is present in most igneous and metamorphic rocks.

GALENA forms cubic crystals with a characteristic stepped pattern caused by complexities in the mineral’s crystal structure. Galena has a metallic luster, and is gray to silver in color. It contains large amounts of the element lead, so it is very dense. Galena is commonly mined and processed for lead, however, some galena crystals contain up to 1% silver. Galena is thus also an important source of silver.

FELDSPAR has a complex, roughly rhombohedral crystal shape. There are many types of feldspars including plagioclase (white) and orthoclase (pink-orange). Although opaque, feldspar crystals have a glassy luster. Quartz and steel will scratch feldspar. Feldspar is a common mineral in igneous and metamorphic rocks. Feldspars are used in making ceramics, as a building material, and as gemstones (the variety moonstone).

ULEXITE grows in fibrous crystals. This gives the mineral a special property; for complex optical reasons, images can travel along the fibrous crystals with little distortion. For this reason, ulexite is often called "TV rock," although it is a mineral. Ulexite is white, and a source of the element boron. Ulexite precipitates from lakes in arid regions due to evaporation. The lakes form only during rainy seasons due to runoff from nearby mountains. Ulexite is used to make some detergents, especially for washing clothes

HEMATITE crystals tend to be very small. This mineral is metallic; it may either appear as a shiny steel color or a dull red. When scratched on porcelain, hematite shows a red-brown streak. Hematite gets its name because of this color, from a Greek word meaning "blood_like." Ancient superstition held that large deposits of hematite formed from the blood that flowed into the ground after large battles. It contains large amounts of iron, so hematite is quite dense. Hematite is an important ore of iron and its red color lends itself well for use as a pigment.

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