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Introduction to Rock-Forming Minerals

• The presentation is about rock-forming minerals, presented by Princess Portia and Shai Lourece.
• The objectives are to identify common rock-forming minerals using their physical and chemical properties and identify minerals important to society.

What is a Mineral?

• A mineral is a naturally occurring, inorganic, homogeneous solid with a definite chemical composition and an ordered crystalline structure.
• Most minerals have distinctive characteristics, however, some are similar and require further examination of physical properties for correct identification.

Physical Properties of Minerals

• Several techniques are used to identify minerals based on physical properties.
• Small minerals require high-powered instruments like microscopes and X-ray diffractometers (XRDs).
• Large minerals can be identified based on their physical properties.
• Geologists commonly use physical properties such as color, streak, luster, crystal habit, cleavage, fracture, hardness, and specific gravity to identify minerals.

Color

• The color of a mineral is due to reflected wavelengths of light perceived by the observer.
• It's the most noticeable property.
• However, a mineral's color is not a reliable diagnostic property for all minerals due to impurities.
• Minerals can be classified into idiochromatic (self-colored), allochromatic (impurity-colored), and pseudochromatic (diffraction-colored).
• Examples of idiochromatic minerals include malachite (always green), rhodochrosite (always red), and sulfur (always yellow).

Streak

• The streak is the color of a mineral's powdered form.
• It is more reliable than color for mineral identification because the streak color is always the same.

Luster

• Luster is the appearance of a mineral's surface, dependent on how it reflects light.
• Common types include pearly, silky, dull, resinous, earthy, adamantine, vitreous (glassy), and metallic.

Crystal Habit

• Crystal habit is the characteristic shape in which a mineral grows, reflecting its internal crystal structure.
• Common habits include acicular, blocky, tabular, fibrous, bladed, dendritic, and prismatic.

Cleavage

• Cleavage is the tendency of some minerals to break along flat surfaces with the weakest atomic bonding.
• Cleavage surfaces tend to occur repeatedly as parallel planes at crystal breaks, which constitute a set or direction of cleavage.

Fracture

• Fracture is the pattern in which a mineral breaks aside from its cleavage planes when atomic bonds are of equal strength.
• Various types include conchoidal, jagged, uneven, and splintery.

Hardness

• Hardness is a mineral's resistance to scratching.
• It's measured using Mohs scale, a relative scale ranging from 1 (softest, talc) to 10 (hardest, diamond).

Specific Gravity

• Specific gravity is the ratio of a mineral's weight to the weight of an equal volume of water.
• The size of a mineral sample is independent of its specific gravity.

Chemical Properties of Minerals

• All minerals can be represented by a chemical formula that shows the proportions of atoms that compose them.
• Quartz (SiO₂), for example, has a continuous framework of silicon-oxygen tetrahedra.
• Chemical properties like solubility and melting point are also used to describe a mineral.

Mineral Groups

• Thousands of minerals have been identified.
• Geologists group them based on their chemical composition.
• Nine broad groups are discussed (e.g., elements, sulfides, oxides).

Analysis of Minerals

• Wet chemical analysis and spectroscopic techniques (AAS, ICP, XRF, XRD) are used to analyze mineral composition and structure, including identifying carbonates.

Common Rock-Forming Minerals

• Quartz, feldspar, mica, pyroxene, amphibole, and olivine are the common rock-forming minerals.

Conclusion

• Key points are summarized: the nature of minerals, their physical and chemical properties, and common mineral groups.