物理性能的矿物二: 矿物分析

Polymineralic rocks contain multiple types of mineral grains, while monomineralic rocks are composed of a single mineral. Most rocks are polymineralic. Geologists classify polymineralic rocks using physical properties like color, hardness, magnetism, and acid reactivity, whereas monomineralic rocks are typically classified by crystal form and cleavage.

Streak represents the color of a powdered mineral sample created by dragging it across a porcelain plate. Unlike apparent color, which varies due to impurities and crystal structure, streak is more reproducible because fine grains are randomly oriented and less affected by these factors. This makes streak a more consistent identification tool in the field.

The Mohs hardness scale ranks ten reference minerals by their ability to scratch or be scratched by other materials. A mineral that scratches a reference material is harder than that reference; conversely, a mineral that is scratched is softer. Geologists test hardness by attempting to scratch glass, which sits near the middle of the scale, then rank samples accordingly.

Luster is a subjective measure of how a mineral reflects light, divided into two categories: metallic minerals that are shiny and reflective, and non-metallic minerals that appear dull. Luster depends on a mineral's atomic structure and chemical composition, making it a useful field identification property alongside other physical characteristics.

Magnetite is the primary mineral that exhibits ferromagnetism. To test for magnetism, flake mineral grains and observe whether a bar magnet picks them up. Additionally, place the mineral sample near a compass needle with about six inches of space, then slowly decrease the distance. If magnetic, the compass needle will point toward the sample as proximity increases.

The acid reactivity test identifies carbonate minerals by observing their reaction with dilute acid. Calcite is the most common carbonate mineral that reacts with acid. This simple test helps geologists quickly classify polymineralic rocks and mineral samples in the field without requiring advanced laboratory equipment.

Advanced techniques like X-ray diffraction (XRD) enable detailed characterization of crystal structure and material composition beyond field tests. Diamond anvil cells reach extremely high pressures to synthesize and analyze new phases of matter. These methods provide precise structural information useful for applications like lithium ion battery development, complementing traditional physical property testing.