Rocks and Minerals
92 flashcards by MentisLibrary
Identify specimens the way geologists do, using hardness, streak, luster, and cleavage. Covers the common minerals and rock types you will actually find, plus the field tests and tools that settle an identification.
- What five properties should you test first when identifying an unknown mineral?
- Hardness, streak, luster, cleavage or fracture, and color
- Why is color the least reliable property for identifying a mineral?
- Tiny amounts of impurities can change color completely while the mineral stays the same
- What is streak and how do you test it?
- The color of a mineral's powder, tested by dragging it across an unglazed porcelain plate
- Why is streak more reliable than surface color?
- The powdered color stays constant even when surface color and tarnish vary
- What is luster and what are its two broad categories?
- How light reflects from a mineral surface, described as metallic or nonmetallic
- What does vitreous luster look like?
- Glassy, like broken window glass
- What does adamantine luster describe?
- A brilliant, sparkling reflection typical of very high refractive index minerals
- What is the difference between cleavage and fracture?
- Cleavage breaks along flat planes of weak bonding; fracture breaks along irregular surfaces
- What is conchoidal fracture?
- Curved, shell-like breakage surfaces
- How is cleavage described when reporting a mineral?
- By the number of directions and the angles between them, plus quality such as perfect, good, or poor
- What are the ten reference minerals of the Mohs scale in order?
- Talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, diamond
- What common objects are used as field hardness testers?
- A fingernail at about 2.5, a copper coin at about 3.5, a steel knife or nail at about 5.5, and glass at about 5.5
- Which mineral is the softest on the Mohs scale and feels soapy?
- Talc
- Which mineral is the hardest natural substance and is pure carbon?
- Diamond
- Which mineral has hardness 7, no cleavage, conchoidal fracture, and hexagonal crystals with pointed ends?
- Quartz
- Which mineral fizzes vigorously in dilute hydrochloric acid and shows three cleavage directions not at right angles?
- Calcite
- Which carbonate mineral fizzes in acid only when powdered?
- Dolomite
- Which mineral has perfect cubic cleavage and a distinctly salty taste?
- Halite
- Which mineral has one direction of cleavage, hardness 2, and forms the raw material for plaster and drywall?
- Gypsum
- Which mineral has hardness 4, four directions of octahedral cleavage, and often glows under ultraviolet light?
- Fluorite
- Which mineral is the reference for hardness 5 and is the main mineral of bones and teeth?
- Apatite
- Which feldspar is pink to salmon and shows two cleavage directions meeting at about 90 degrees?
- Orthoclase, a potassium feldspar
- Which feldspar is usually white to gray and shows fine parallel striations on cleavage faces?
- Plagioclase
- Which mineral splits into thin transparent flexible sheets?
- Muscovite mica
- Which dark mica splits into flexible black to brown sheets?
- Biotite
- Which soft black mineral marks paper, feels greasy, and conducts electricity?
- Graphite
- Which mineral has a bright brassy color, hardness 6, and often forms cubes with striated faces?
- Pyrite
- How can you distinguish gold from pyrite in the field?
- Gold is soft, malleable, and very dense with a golden yellow streak; pyrite is hard, brittle, and streaks greenish black
- Which mineral is a heavy gray metallic sulfide with perfect cubic cleavage and is the main ore of lead?
- Galena
- Which iron oxide gives a reddish brown streak regardless of its surface appearance?
- Hematite