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:

• Small red spheres represent silicon (Si) atoms.
• Larger 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 the following.

• Noble gases in the last column on the right (light blue): helium neon, argon, krypton
• Alkali metals in the first column on the left (red): lithium, sodium, potassium.
• Nonmetals on the right side of the table (green/yellow): carbon, phosphorus, sulphur, selenium, nitrogen, oxygen, flourine, chlorine, bromine.

Each element is shown in a 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)

Figure 2.1.6 Electron configuration of sodium and chlorine atoms

The top two diagrams show the electron configuration of sodium and chlorine.

• Sodium atoms have 11 electrons: 2 in the first shell, 8 in the second, and 1 in the outermost (third) shell
• Chlorine atoms have 17 electrons: 2 in the first shell, 8 in the second, and 7 in the outermost (third) shell. 

The bottom two diagrams show a sodium ion giving up one electron (from its outmost shell) to become a cation, while the chlorine ion accepts the electron into its outermost shell - becoming chloride, which is an anion.

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:
  • A color gradient bar from yellow(top, ~1300°C) to deep red (bottom, ~750°C) represents the cooling of magma.
  • An arrow labeled “Cooling” points downward, indicating decreasing temperature.
• Discontinuous branch:
  • 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:
  • Involves plagioclase feldspar, which evolves from
    • Calcium-rich at high temperatures to
    • Sodium-rich at lower temperatures
• Final minerals (bottom center), which crystallize at the lowest temperatures and are common in felsic rocks:
  • Potassium feldspar
  • Muscovite
  • Quartz
• Rock types, listed on the 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 2.5.3 Sediment Sorting

• Very poorly sorted: Example shows very large clasts among tiny specks and moderately sized clasts.
• Poorly sorted: Example shows moderately sized clasts among many smaller clasts.
• Moderately sorted: Example shows moderately sized clasts with a few smaller clasts and tiny specks.
• Well sorted: Example shows clasts with little variation in size.
• Very well sorted: Example shows clasts of close to identical sizes.

Figure 2.6.10 Serpentinite Outcrops

This geologic map of California emphasizes the spatial distribution of serpentinite, California's state rock. The entire state is shown with clear coastal boundaries and fault traces. The serpentinite outcrops (~245–65 Ma) appear as small purple patches. They are especially concentrated along the Coast Ranges, Klamath Mountains, and parts of the Sierra Nevada foothills.

The figure place the Precambrian rocks in the context of California’s overall geologic framework. 

• Cenozoic (0–65 Ma)
  • Cenozoic nonmarine (continental) sedimentary rocks and alluvial deposits (~0.011–65 Ma). These rocks are shown mainly in large lowland areas, especially the Central Valley and other broad interior basins. They also appear in smaller patches along major river valleys and coastal lowlands.
  • Cenozoic marine sedimentary rocks (~1.6–65 Ma). These rocks occur primarily along the coastal regions of California. They form discontinuous belts near the shoreline and adjacent offshore-margin areas.
  • Cenozoic volcanic rocks (~1.6–65 Ma). These rocks are concentrated in northeastern California and parts of eastern California. Smaller volcanic areas also appear scattered in the Coast Ranges and southern California.
• Mezozoic (65–245 Ma)
  • Late Mesozoic (latest Jurassic and Cretaceous) marine sedimentary rocks; Great Valley Sequence and related rocks (~145–65 Ma). These rocks form a long, continuous band along the western side of the Central Valley. They are positioned between the Coast Ranges and the Sierra Nevada.
  • Mesozoic sedimentary and volcanic rocks in places strongly metamorphosed (~245–65 Ma). These rocks occur mainly in the Sierra Nevada foothills and parts of the Klamath Mountains. They appear as elongated belts adjacent to large areas of granitic rocks.
  • Late Mesozoic (latest Jurassic and Cretaceous) Franciscan Complex (~145–65 Ma). This unit is widely distributed throughout the Coast Ranges of California. It forms a broad, irregular belt parallel to the coastline.
  • Granitic rocks chiefly Mesozoic (~245–65 Ma). These rocks dominate the Sierra Nevada and form a large, continuous region there. Smaller granitic bodies also appear in southern California and parts of the Coast Ranges.
  • Serpentinized ultramafic rocks chiefly Mesozoic . These rocks occur as narrow, scattered bodies primarily within the Coast Ranges and the Klamath Mountains. They are also present in small patches along major fault zones.
• Paleozoic (245–570 Ma)
  • Paleozoic sedimentary and volcanic rocks; in places strongly metamorphosed (~570–245 Ma). These rocks are found in eastern California and in parts of the Klamath Mountains. They also appear in smaller, isolated areas within mountain ranges.
• Precambian (older than 570 Ma)
  • Precambrian rocks of all types including coarse-grained intrusives (>570 Ma). These rocks are restricted mainly to southeastern California. They appear as isolated patches within desert mountain ranges.
• Pre-Cenozoic (>65 Ma)
  • Pre-Cenozoic metamorphic rocks of unknown age (>65 Ma). These rocks are shown in scattered areas within mountain belts across the state. They commonly occur adjacent to granitic rocks in the Sierra Nevada and southern California.