ES Chapter 5 Review Questions
On what basis do mineralogists organize silicate minerals into distinct groups? What type of silicate group does the diagram portray?
- Independent/Single Tetrahedron: No "O" atom sharing; olivine, garnet - Single Chain: 2 "O" atoms are shared; pyroxene group (augite) - Double Chain: 2 or 3 "O" atoms are shared; amphibole group (hornblende) - Sheet: 3 "O" atoms are shared; mica group (muscovite, biotite), clay group (kaolinite) - 3-D Framework: 4 "O" atoms are shared, most common type of silicate; feldspar group (orthoclase, plagioclase), quartz
Describe the several ways that minerals can form.
-Solidification from a melt -precipitation, directly from a solution (dry-up seawater) -solid-state diffusion -biomineralization -minerals can precipitate directly from a gas
Why are some minerals considered gemstones? How do gem cutters make the facets on a gem?
To qualify as a gem, the specimen should be hard and tough to resist scratching and have beautiful clarity color or 'fire'. Value is based on rarity and rare quality; gem cutters use a faceting machine (faces are made by grinding the stone on a lap)
Why isn't glass considered to be a mineral?
Both minerals and glass are solids. But minerals are crystalline, and glass is not. The ions, atoms and molecules in glass are very disorderly. Glass does not match this characteristic of an atom- orderly order.
How do you distinguish cleavage planes from crystal faces on a mineral? How does each type of surface form?
Cleavage surfaces form at the weakest part of a crystal - crystals form with a "heavier/stronger" side and the side that is neglected has ability to break off and form a cleavage surface. Crystal faces are the edges of crystals. Crystal faces move outward but maintain the same orientation.
List and define the principal physical properties used to identify a mineral.
Color, streak- color of a mineral. crushed onto porcelain. luster- shine. hardness- scratching resistance. specific gravity- mass per volume. crystal habit- shape of the crystal. cleavage- crystal that breaks in a predetermined place. Fracture- curving surfacecs that break without cleavage.
On what basis do geologists separate minerals into classes?
Dominant anion (halides, oxides, sulfides)
How can you determine the hardness of a mineral? What is the Mohs hardness scale?
If it can scratch or becomes scratch from another mineral; Moh's hardness scale: a list of ten minerals in a sequence of relative hardness, with which other minerals can be compared
Salt is a mineral, but the plastic making up an inexpensive pen is not. Why not?
It does not have any mineral characteristics; not naturally occurring
How does the bonding in mica determine cleavage in mica crystals?
Micas tend to cleave between the silicon-oxygen structures, rather than across them, because the silicon-oxygen bonds are strong. The micas' sheet structure causes them to cleave flat plates.
What is a mineral, as geologists understand the term? How does this definition differ from the everyday usage of the word?
Mineral to a geologist- a naturally occurring solid, formed by geologic process that has a crystalline structure and a definable chemical composition. Def of mineral: -naturally occurring -formed by a geologic process -solid -crystalline structure -definable chemical composition -inorganic
Why do some minerals occur as euhedral crystals, whereas others occur as anhedral grains?
Minerals without well-formed crystal faces are anhedral grains. If a mineral's growth is unimpeded so that it displays well-formed crystal faces, then it is a euhedral crystal. The surface crystals of a geode, a mineral-lined cavity in rock, may be euhedral.
