Rock Sample Identification
1. ROCK TYPE: IGNEOUS, SEDIMENTARY, or METAMORPHIC)
2. SUB-CLASS: If IGNEOUS,
If SEDIMENTARY, Clastic or Chemical
If METAMORPHIC, Foliated or Non-Foliated
3. ROCK NAME: As listed in your study guide - only rocks assigned in class will be on the exam. Do not waste your time studying the rocks that were not assigned!
How do you prepare for this lab exam? Practice! Practice! Practice!
A. Be familiar with the general visual attributes of each rock type (igneous, sedimentary, and metamorphic) and how these contrast with each other.
B. Focus LESS on the rock NAME, and MORE on the ROCK TYPE. If you guess the wrong rock name first, and then base your rock type and subclassification upon a mistaken rock name, you are likely to miss all 3 points for that sample. Therefore, identify the rock type first.
1. You should base your identification upon some solid evidence. Think logically, in small steps: "This rock has sharp, angular, intergrown crystals with no pore space, and it scratches glass. Therefore it's igneous. The crystals are coarse due to slow cooling, which happened far below the ground - therefore it's plutonic. The rock is almost black in color, so it must be mafic. The rock name is therefore gabbro. Know what to do with those testing tools (acid bottle, glass plate).
2. Associate a rock name with the correct rock type. For example:
sandstone = sedimentary (Evidence: rounded grains of quartz sand)
basalt = igneous (Evidence: scratches glass, dark = mafic, fine-grained = volcanic)
marble = metamorphic (Evidence: fizzes - acid reaction = carbonate, shiny + no fossils)
3. The most difficult rocks to identify are the fine-grained rocks. You need to be able to distinguish between those which are made of silicates (volcanic rocks, which are hard enough to scratch glass) and those made out of clay minerals (shales, which are much softer), or lime mud (lithographic limestone, which is soft and reacts by fizzing with acid). Coal will not only be very soft, but also light in weight, being made of organic material.
4. Trays of rock samples will be held on reserve at the Testing Center, Room A-135, which is open from Monday through Thursday until 8:00 PM, and on Friday until 4:00 PM. You are encouraged to study these samples on your own time.
NOTE: The study samples at the Testing Center are used repeatedly by many classes. Over time, some of the samples may become lost, or damaged such that the number label falls off. If this happens, e-mail me at firstname.lastname@example.org and describe exactly what rock specimen number(s) you think are missing, and I will try to replace what is missing or damaged before class.. I am only on campus on the 2 nights per week that I teach.