2.8: Detailed Figure Descriptions

Figure 2.1.3 SiO₂ Quartz

This image illustrates the regular repeating atomic structure of a silicate mineral in two dimensions. The structure is represented at the atomic level.

Visual Elements:

• Atoms are shown as colored spheres:
• Red spheres represent silicon (Si) atoms.
• Light blue spheres represent oxygen (O) atoms.
• The atoms are connected by lines indicating covalent bonds.

Structural Arrangement:

• The silicon and oxygen atoms form tetrahedral units, where one silicon atom is bonded to four oxygen atoms.
• These tetrahedra are arranged in a hexagonal pattern, sharing three of their oxygen atoms with adjacent tetrahedra.

Figure 2.1.5 First Four Rows of the Periodic Table

This diagram presents the first four periods (rows) of the periodic table, including elements with atomic numbers 1–36. Elements are arranged left to right by increasing atomic number. Color coding visually differentiates element types, such as noble gases (light blue), alkali metals (red), and nonmetals (green/yellow).

Each element is shown in a colored square containing:

• The element symbol (e.g., H for hydrogen)
• The element name (e.g., hydrogen)
• The atomic number (top left)
• The atomic weight (bottom)

Example callouts highlight chromium (Cr) to indicate atomic number 24 and atomic weight 52.00.

Figure 2.4.1 Bowen's Reaction Series

This diagram illustrates Bowen’s Reaction Series, a conceptual model showing how different silicate minerals crystallize from magma as it cools from around 1300°C to 750°C. The series splits into two branches—discontinuous and continuous—with corresponding mineral types and associated igneous rock classifications.

Layout Description:

• Vertical Temperature Gradient (Left):
  • A color gradient bar from red (top, ~1300°C) to purple (bottom, ~750°C) represents the cooling of magma.
  • An arrow labeled “Cooling” points downward, indicating decreasing temperature.
• Discontinuous Branch (Left Side):
  • Minerals form in sequence as temperature decreases:
    • Olivine
    • Pyroxene
    • Amphibole
    • Biotite
  • Each mineral forms, then reacts with the melt to form the next.
• Continuous Branch (Right Side):
  • Involves plagioclase feldspar, which evolves from:
    • Calcium-rich at high temperatures
    • To Sodium-rich at lower temperatures
• Final Crystallizing Minerals (Bottom Center):
  • Potassium feldspar
  • Muscovite
  • Quartz
  • These crystallize at the lowest temperatures and are common in felsic rocks.
• Rock Types (Far Right):
  • Classification of igneous rocks by their dominant minerals:
    • Ultramafic (e.g., peridotite)
    • Mafic (e.g., gabbro, basalt)
    • Intermediate (e.g., diorite, andesite)
    • Felsic (e.g., granite, rhyolite)

Figure 2.4.3 Common Igneous Rocks

This image presents a side-by-side comparison of six igneous rock samples, arranged by both composition (mafic, intermediate, felsic) and type (intrusive vs. extrusive). Each sample shows a close-up of the rock's texture, helping students visually identify mineral composition and grain size.

Category	Intrusive Rock (Top Row)	Extrusive Rock (Bottom Row)
Mafic	Gabbro	Basalt
Intermediate	Diorite	Andesite
Felsic	Granite	Rhyolite

Top Row (Intrusive Rocks):

• Gabbro (Mafic): Dark greenish-black with coarse grains of light-colored minerals.
• Diorite (Intermediate): Salt-and-pepper texture with nearly equal light and dark minerals.
• Granite (Felsic): Light-colored with large visible crystals of quartz and feldspar.

Bottom Row (Extrusive Rocks):

• Basalt (Mafic): Very dark gray to black with fine-grained texture.
• Andesite (Intermediate): Grayish, intermediate texture with subtle mineral contrast.
• Rhyolite (Felsic): Light pink to white, fine-grained and uniform.

Figure 2.4.4 Igneous Rock Classification by Mineral Composition

This diagram shows the relative mineral composition of igneous rocks across the spectrum from felsic to ultramafic. The vertical axis represents mineral percent (0–100%), while the horizontal axis categorizes rocks by composition and texture (intrusive vs. extrusive).

Horizontal Rock Categories from left to right:

• Felsic: Granite / Rhyolite
• Intermediate: Diorite / Andesite
• Mafic: Gabbro / Basalt
• Ultramafic: Peridotite / Komatiite

Vertical (Y) axis is labeled “Mineral percent” from 0% (bottom) to 100% (top). The following table summarizes the four major compositions of igneous rocks (felsic, intermediate, mafic, ultramafic) and the proportions of common minerals in each. The names for both intrusive and extrusive rock names are summarized at the bottom of the table.

Igneous compositions by mineral proportion and their corresponding intrusive and extrusive rock names.

	Felsic	Intermediate	Mafic	Ultramafic
K-feldspar	0 to 35%	0%	0%	0%
Quartz	25 to 35%	0 to 25%	0%	0%
Plagioclase feldspar	25 to 50%	50 to 70%	0 to 50%	0%
Biotite and/or amphibole	0 to 20%	20 to 40%	0 to 30%	0%
Pyroxene	0%	0 to 20%	20 to 75%	0% to 75%
Olivine	0%	0%	0 to 25 %	25% to 100%
Intrusive rock name	Granite	Diorite	Gabbro	Peridotite
Extrusive rock name	Rhyolite	Andesite	Basalt	Komatiite

Figure 2.5.2 Sediment Roundness

This diagram illustrates how the shape of sediment particles changes due to abrasion during transportation. The process is key in sedimentology and helps geologists interpret the transport history and depositional environment of sedimentary rocks.

The image is organized left to right, showing a progression of particle shapes:

• Angular
• Subangular
• Subrounded
• Rounded

A horizontal gradient arrow runs beneath the images labeled "Increasing abrasion during transportation" from left (white) to right (black), indicating progressive rounding over time and distance.

Description of Each Shape Category:

• Angular:
  • Sharp corners and irregular edges.
  • Indicates minimal transport from source.
• Subangular:
  • Still has corners but less pronounced.
  • Suggests short transport or limited abrasion.
• Subrounded:
  • More smoothed edges, rounded but not fully.
  • Implies moderate transport distance or time.
• Rounded:
  • Smooth and curved, no sharp corners.
  • Represents long-distance or prolonged transport.

Figure 2.6.10 Serpentinite Outcrops

This image is a statewide geologic map of California that emphasizes the spatial distribution of serpentinite, California's state rock. The serpentinite outcrops are marked in purple. The entire state of California is shown with clear coastal boundaries and fault traces.

Serpentinite outcrops appear as small purple patches, especially concentrated along the Coast Ranges, Klamath Mountains, and parts of the Sierra Nevada foothills.

Other Units:

• Sedimentary rocks (in yellow, tan, and pink)
• Volcanic rocks (pale orange)
• Metamorphic rocks (light and dark grays)
• Igneous rocks (peach and red)

Each unit corresponds to different geologic periods, from the Precambrian to the Cenozoic.

Legend (Top Right) Titled "Correlation of Map Units", with vertical bars aligning rock types to the geologic time scale (in millions of years):

• Divided into two broad categories:
  • Sedimentary and Volcanic Rocks
  • Intrusive Igneous and Metamorphic Rocks
• Serpentinite is identified under "Serpentinized ultramafic rocks chiefly Mesozoic".
• Structural Features:
  • Fault traces are indicated with solid or dashed black lines, depending on whether they are exposed or concealed.
  • Some of these faults trace significant geological boundaries, such as the San Andreas Fault.