Rocks and minerals are the building blocks of the Earth Crust. Learning how to identify the main types of rocks and their minerals will help students understand the geology of the Guadalupes and how a beautiful reef can transform into a mountain.
The learner will:
• Learn about mineral composition and identification.
• Understand the rock cycle and identify some common rocks in each group.
• Apply this knowledge to geology in the Guadalupe Mountains region.
The Earth's building blocks are minerals and rocks. Minerals, of which rocks are composed, are defined by standard criteria: 1) specific chemical composition, 2) inorganic, 3) regular crystalline structure, 4) naturally occurring, and 5) solid. While it is tempting to use color to determine the type of mineral, many of the same minerals come in a variety of colors so other characteristics must be used. Diagnostic tests for identifying minerals use properties: hardness (on a scale from one being the softest mineral, talc, to ten, a diamond, the hardest mineral found), streak (the color of the mineral´s powder when you rub it on a porcelain plate), cleavage (the ways a mineral naturally breaks), effervescence (reaction of mineral to weak HCl, hydrochloric acid), magnetism (attracted to magnets or not), taste (however some minerals are toxic, so you don't want to lick them all) and fluorescence (fluorescence when exposed to an ultraviolet light or not). While there are many different minerals found throughout the world, some minerals specific to the Guadalupe Mountains, Delaware Basin, and Carlsbad Caverns are calcite, dolomite, gypsum, halite, sulfur, and pyrite. The majority of the Earth's surface is composed of quartz and feldspar, two other minerals that are not as common in this area of carbonates.
Rocks, in turn, are composed of minerals. There are three types of rocks: 1) igneous rocks where the interlocking minerals crystallize out of molten material, 2) sedimentary rocks composed of cemented physically-weathered sediments derived from other rocks or chemically precipitated from saturated solutions, and finally 3) metamorphic rocks, which are pressure and temperature "cooked" versions of any of these three types of rock. Fossils can be found in sedimentary rocks and, occasionally, in some metamorphic rocks too. The most common rock in the area is limestone, which is composed of the mineral calcite.
Identification of rocks and minerals allows geologists to produce geologic maps. This knowledge can aid in the understanding of the paleoenvironment and time period in which the rocks and minerals formed. This activity will introduce common rocks and minerals found in the Guadalupe Mountains and Carlsbad Cavern region as well as others that are common elsewhere. Identification of samples will also enhance students' observational and classification skills. Once the students have identified the rocks and minerals, they will be able to understand a geologic map.
Materials for this lesson include minerals and rocks kits, geologic maps and graphic organizers (flow chart, Venn diagram and rock cycle chart).
• Explain that the Earth is composed of rocks, which are composed of minerals. Define each.
• Define the properties of minerals and explain that these characteristics may be examined and tested on hand samples.
• Pass out the mineral samples to identify with the testing kits and the flow chart. Explain that these are just a few of the minerals that are represented in the Guadalupe Mountains—emphasize that there are many more in the area and the world!
• Let the students work together to identify the different minerals using the standard tests and have them record the names and some characteristics in their notebooks.
• After checking students’ answers, have students complete a Venn diagram for common minerals in the region (i.e. calcite, dolomite, and gypsum).
• Explain the rock cycle and that rocks are composed of different minerals. While there are three different types of rocks, for the Guadalupe Mountains and Carlsbad Cavern story, we are mainly interested in sedimentary rocks so these will be the majority of the rocks the students will identify.
• Once the rock samples are passed out and the students are divided into groups, help the class separate the different rock types.
• Pass out the three different rock flow charts and have students use the charts to identify the different rock samples. They should write descriptions and identifications in their science notebooks. The students may also look for their minerals in the rocks, but keep the samples separate to avoid confusion.
• Using the Guadalupe Mountains and Carlsbad Caverns National Park geology maps and formation descriptions, have students link the geologic formations with their rock and mineral characterizations. Students should record these descriptions of each unit in their science notebooks.
• Lab report
• Data table of identified minerals and rocks
• Venn Diagram of several local minerals
• Geologic map interpretation
Students can see samples of the rocks found in the Guadalupes at the Pine Springs Visitors Center museum as well as through any of the trails recommended. They can learn that fossils can be found mainly in sedimentary rocks and be able to see the minerals and rocks that formed the ancient reef.
• Have students draw a schematic diagram of the backreef, reef, and forereef area. Label the different units and minerals found in each environment (similar to the schematic cross-section used in Lesson 1).
• Students should list different environments where each type of sedimentary rock is found (i.e. sandstone may be formed in rivers, beaches, mountains, deltas, etc.) to show the complexity of paleoenvironmental reconstructions using only rock types.
• Have students identify minerals used in everyday products (i.e. drywall, toothpaste, lipstick, milkshakes, vitamins, etc.).
Beaubouef, R.T., Rossen, C, Zelt, F.B, Sullivan, M.D., Mohrig D.C. and D.C. Jeanette. 1999. “Deep-Water Sandstones, Brushy Canyon Formation, West Texas.” AAPG Field Guide #40.
Marshak, S. 2001. Earth Portrait of a Planet. New York: W.W. Norton & Co.
USGS Learning Web, Rocks and minerals web page: http://interactive2.usgs.gov/learningweb/explorer/topic_rocks.htm
Additional reading and other resources:
Amethyst Galleries Inc. Mineral Gallery web page: http://mineral.galleries.com/
USGS Rocks and Minerals web page: http://geology.er.usgs.gov/eastern/rocks.html
Mineral, rock, crystal structure, chemical composition, hardness, luster, cleavage, carbonates, rock cycle, igneous rock, metamorphic rock, sediment, clast, sedimentary rock, metamorphism, magma, crystallization, cementation, evaporite, metallic, nonmetallic, striations, transparent, translucent, physical weathering, chemical weathering, erosion, rock cycle, basalt, granite, trona, limestone, conglomerate, sandstone, shale, coquina, coal, gneiss, schist, marble, slate, foliated, crystalline, texture, vesicular, ooids, pebbles, sand, gravel, grain size, clay, organic material, ultraviolet light, hydrochloric acid, effervescence, streak, calcite, dolomite, gypsum, halite, sulfur, pyrite, muscovite mica, orthoclase feldspar, quartz