Lecture 3 Flashcards
How do geologists define a mineral?
A mineral must (1) form by natural geologic processes, (2) be solid, (3) have a crystalline structure, (4) have a definable chemical composition, and (5) be inorganic.
What is the difference between a rock and a mineral?
A rock is an aggregate of one or more minerals (or mineral-like materials), whereas a mineral is a single substance with uniform composition and properties.
Why is glass not considered a mineral?
Glass is a solid but does not have an orderly atomic arrangement; its atoms are disordered (amorphous), so it does not meet the crystalline structure requirement for minerals.
What is mineral hardness, and what scale is used to measure it?
Hardness is a mineral’s resistance to scratching or abrasion, determined by the strength of its atomic bonds. The Mohs scale (from 1 = talc to 10 = diamond) is used to measure it.
What is crystal habit?
Crystal habit is the ideal shape a mineral’s crystals form if they grow freely under optimal conditions (e.g., cubic, prismatic, dodecahedral).
How does cleavage differ from fracture?
Cleavage is when a mineral breaks along planes of weakness in its atomic structure, producing smooth surfaces. Fracture is an irregular break that occurs when no such planes exist.
What is tenacity in mineral identification?
Tenacity describes how a mineral responds to stress (e.g., bending, breaking). Some minerals are brittle, others may be malleable or flexible, depending on their bonding.
What is diaphaneity, and what are its three categories?
Diaphaneity is how well a mineral transmits light. The three categories are: *transparent (clear view), *translucent (light passes, but images are hazy), *opaque (no light passes).
What is lustre, and what two main types do we distinguish?
Lustre is how light reflects off a mineral’s surface. The two main types are: *metallic (reflects like polished metal), *nonmetallic (subtypes include vitreous, pearly, silky, etc.).
Why is color alone often unreliable for identifying minerals?
Many minerals display various colors due to trace impurities or structural variations, so color can mislead. Other properties (e.g., streak, hardness, cleavage) are more diagnostic.
What is streak, and why is it useful?
Streak is the color of a mineral in its powdered form (found by rubbing on an unglazed porcelain plate). It tends to be more consistent than a mineral’s surface color and is thus more reliable.
How is density different from specific gravity?
Density (ρ) is mass per unit volume (g/cm³), while specific gravity (G) is the ratio of the mineral’s density to the density of water (dimensionless). Numerically, they are often similar.
Name two quick chemical or physical tests that identify certain minerals.
*Magnetism (e.g., magnetite attracts a magnet) *acid reaction (e.g., calcite fizzes with dilute HCl) are common quick tests.
What are some ‘sensory’ mineral tests?
*Odor (sulfur smells like rotten eggs) *taste (halite is salty) *feel (graphite or talc can be greasy) are examples of sensory tests.
How does chemical bonding influence mineral properties?
Bond type (ionic, covalent, metallic, van der Waals) affects hardness, cleavage, melting point, conductivity, etc. Stronger bonds (covalent/ionic) often yield harder, more brittle minerals, while weaker bonds (metallic/van der Waals) can allow malleability or softness.
Give an example of a mineral with ionic bonds and its properties.
Halite (NaCl) uses ionic bonding (electron exchange), giving it cubic cleavage and making it easily dissolved in water.
Which mineral is entirely covalently bonded, and what is its defining property?
Diamond has only carbon atoms sharing electrons (covalent bonds), making it the hardest known natural mineral (Mohs hardness of 10).
Which bond type allows electrons to move freely, and what does this imply?
Metallic bonds have free-moving electrons, making minerals (e.g., native copper) good conductors and often malleable or ductile.
What are van der Waals bonds, and can you give an example of a mineral that has them?
Van der Waals bonds are weak intermolecular forces. Graphite is an example: its layers of carbon sheets are strongly bonded internally but weakly bonded between sheets, so it’s soft.
Why are silicate minerals (like quartz and feldspar) so important?
They form most of Earth’s crust and mantle, built around silica tetrahedra (SiO₄). Their arrangement (isolated, chains, sheets, frameworks) produces varied physical properties. Geologists use them to interpret rock origins and conditions of formation.
