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2: Minerals and Rocks

Last updated

Jan 10, 2025
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- 1.2: Geologic Map Symbols
- 2.1: Minerals

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Introduction to Minerals and Rocks

Before we can begin to discuss rocks and the rock materials that make up the state of California, we must address the building blocks of rocks: minerals; and the components that make up minerals: atoms and elements.

Minerals are all around us: the graphite in your pencil, the salt on your table, the plaster on your walls, and the trace amounts of gold (Figure $\PageIndex{1}$ ) in your computer. Minerals can be found in a wide variety of consumer products including paper, medicine, processed foods, cosmetics, electronic devices, and many more. Everything made of metal is also derived from minerals.

A large sample of naturally occurring gold. — Figure $\PageIndex{1}$ : California’s State Mineral, gold, from a gold-quartz hydrothermal vein in the "motherlode" of California, USA. (public display, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA). "Gold from quartz-gold hydrothermal vein (California, USA) 1" by James St. John via Flickr is licensed under CC BY 2.0.

A rock is a consolidated aggregate of minerals. By consolidated, we mean hard and strong. A mixture of minerals implies the presence of more than one mineral grain, but not necessarily more than one type of mineral. A rock can be composed of only one type of mineral (e.g., limestone is commonly made up of only calcite), but most rocks are composed of several different minerals. A rock can also include non-minerals, such as fossils or the organic matter within a coal bed.

Rocks are grouped into three main categories based on how they form:

Igneous: formed from the cooling of magma (molten rock)
Sedimentary: formed when weathered fragments of other rocks are buried, compressed, and cemented together, or when minerals precipitate directly from solution
Metamorphic: formed by alteration (due to heat, pressure, and/or chemical action) of a pre-existing rock

This chapter wraps up with a discussion of the distribution of rocks in the state of California, using the Geologic Map of California as our guide.

Learning Objectives

By the end of this chapter, you should be able to:

Describe the ways in which atoms bond to form compounds like minerals.
Differentiate between minerals and rocks.
Be familiar with the three general rock types, how they form, and how they are related to one another through the rock cycle.
Describe the general distribution of rock types across the state of California.

2.1: Minerals
The definition of a mineral encompasses five key characteristics: it must be naturally occurring, inorganic, solid at room temperature, have a regular internal structure, and a defined chemical composition. Minerals are formed by atoms arranged in a crystal lattice and can include elements such as sodium and chlorine forming halite. Minerals are categorized based on their chemical compositions, such as oxides, sulfides, carbonates, and silicates.
2.2: Mineral Properties
This page discusses mineral identification based on chemical composition and crystalline structure, emphasizing physical properties like color, streak, luster, hardness, crystal habit, and cleavage. It highlights the reliability of streak over color, defines luster and hardness with Mohs scale, and discusses cleavage types influenced by atomic arrangement. Examples like graphite and calcite illustrate cleavage distinctions.
2.3: The Rock Cycle
This page explains the three main types of rocks: igneous, sedimentary, and metamorphic, and how they form through geological processes. It discusses the rock cycle, which illustrates the transformation of rocks via uplift, erosion, sedimentation, and other processes. Key steps in the cycle include burial, cementation, and weathering, highlighting the dynamic interactions within Earth's geology.
2.4: Igneous Rocks
This page details the formation and classification of igneous rocks. Igneous rocks form from cooling magma, either extrusively at or near the Earth's surface or intrusively within the crust. Bowen's reaction series describes the order of mineral crystallization in cooling magma.
2.5: Sedimentary Rocks
This page provides a detailed overview of clastic (detrital) sedimentary rocks, which are formed from the accumulation of rock and mineral fragments transported by natural forces and deposited as sediment. It explains the classification of clastic sedimentary rocks based on clast size, roundness, and sorting. The page also touches on other types of sedimentary rocks, including chemical and biochemical sedimentary rocks like limestone and chert.
2.6: Metamorphic Rocks
Metamorphic rocks form through the transformation of pre-existing rocks under heat and pressure, resulting in new minerals or larger crystals. This process often occurs during mountain-building and plate convergence, leading to foliated rocks with aligned mineral bands. Non-foliated metamorphic rocks including quartzite and marble form under lithostatic pressure. The text highlights serpentinite, California's state rock, known for its mineral serpentine.
2.7: Chapter Summary
The page provides an overview of minerals and their properties, including their chemical compositions and types of bonding, as well as a description of the rock cycle and its three main types: igneous, sedimentary, and metamorphic. It also details the formation and identification of igneous rocks, sedimentary rocks, and mentions the presence of geological maps, with an emphasis on California's geological features.
2.8: Detailed Figure Descriptions
Descriptions of complex images within this chapter, as well as additional guidance for users who may have difficulty perceiving images.

Thumbnail: A nugget of gold from the California foothills. "Gold nugget (placer gold) (California, USA)" by James St. John via Flickr is licensed under CC BY.

Introduction to Minerals and Rocks

Learning Objectives

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