Rock Cycle, Minerals, Monsoons, Air Fronts, and Metamorphism

The Rock Cycle

The Rock Cycle: Igneous rocks are formed by the cooling and crystallization of magma. When exposed to weathering agents on the Earth's surface, they decompose. Weathering products are transported and deposited as sediment. During and after deposition, the lithification process occurs, in which sediments become sedimentary rocks. When buried deep underground, under high temperatures and penetrated by chemically active gases and solutions, these rocks are transformed into metamorphic rocks. Metamorphism does not melt the rock, but the minerals change shape and often in nature. If the rock melts, it creates magma. This magma, upon cooling, produces igneous rocks, and a new cycle begins. The cycle can be interrupted and follow paths indicated by the broken arrows.

Identifying Mineral Physical Properties

• Color: To determine a mineral's color, use a streak plate or porcelain biscuit. Rubbing the mineral on it leaves a streak that corresponds to its true color.
• Luster: Also called gloss, this property helps identify certain minerals. It's the reflective power of the mineral's surface when light shines on it. It can be metallic, greasy, matte, and others.
• Translucency: This property allows certain minerals to transmit light more or less easily. Depending on the intensity of light entering and the ease with which we can see objects through it, we can distinguish four types: clear, semi-transparent, translucent, and opaque.
• Thermoluminescence: Several minerals emit light when heated at various temperatures.
• Triboluminescence: Some minerals become bright through friction, percussion, or when reduced to dust.
• Fluorescence: Certain minerals emit light when subjected to ultraviolet rays.
• Phosphorescence: Some minerals continue to emit light after being subjected to ultraviolet rays.
• Cleavage: This property depends on the cohesion of certain minerals. When hit (percussion) or pressured (e.g., with a razor's edge), they separate into sheets or pieces with flat surfaces called cleavage planes.

Uses of Minerals

• Quartz: Jewelry, optical devices, electronics.
• Graphite: Lubricants, pencils, and paint.
• Halite: Food, chemical manufacturing.
• Gypsum: Construction materials.
• Diamond: Cutting, polishing, drilling elements, and jewelry.

Monsoons

Monsoons are periodic changes in wind direction, occurring with each inversion, in the form of violent storms. They are common on the Asian continent. From November to March, the winter monsoon is cold and dry, blowing from the continent to the sea (northeast-southwest). In March or April, the direction changes, and it blows violently from the sea to the mainland; this is the summer monsoon, which is hot and humid.

Air Fronts

When two air masses of different densities and temperatures meet, they form a front, a surface of discontinuity.

• Cold Front: Advances under a warm air mass, pushing it forward or upward.
• Warm Front: Moves at a greater speed, behind or below the mass of cold air.
• Occluded Front: There are three forms: when two cold air masses sandwich a warm one. The warm air mass loses contact with the ground and rises above the cold air.

Secondary Minerals

Secondary or supergene minerals are the result of the alteration of primary minerals in surface areas of the Earth's crust.

Accessory Minerals

Accessory minerals occur in small quantities and do not influence the character of the rock. If present in sufficient quantities to warrant mention, they are called *characteristic minerals*. For example, olivine is a characteristic mineral in olivine basalt or olivine gabbro.

Metamorphic Rock Foliation

• Foliated: These show leafy, slaty, or schistose structures.
• Non-foliated: These do not have the aforementioned feature.