Mineral identification (2)

Chapter Five Weathering: The Breakdown of Rocks... CHAPTER 5: WEATHERING: THE BREAKDOWN OF ROCKS A WEATHERING: PROCESS BY WHICH ROCKS AND MINERALS BREAK DOWN AT OR NEAR THE EARTH’S SUR

Chapter Five

Weathering: The Breakdown of Rocks

CHAPTER 5: WEATHERING: THE

BREAKDOWN OF ROCKS

A) WEATHERING: PROCESS BY WHICH ROCKS AND MINERALS

BREAK DOWN AT OR NEAR THE EARTH’S SURFACE

ΒΕΝΕΦΙΤΣ ΟΦ ΩΕΑΤΗΕΡΙΝΓ: ΠΡΟ∆ΥΧΕΣ ΣΟΙΛΣ (ΜΙΝΕΡΑΛΣ ΑΝ∆ ΕΛΕΜΕΝΤΣ)

∆ΕΤΡΙΜΕΝΤ ΟΦ ΩΕΑΤΗΕΡΙΝΓ: ∆ΕΣΤΡΟΨΣ ΣΤΡΥΧΤΥΡΕΣ ΩΕ ΒΥΙΛ∆

Β) ΕΡΟΣΙΟΝ: ΠΡΟΧΕΣΣ ΒΨ ΩΗΙΧΗ ΜΟςΙΝΓ ΩΑΤΕΡ, ΩΙΝ∆, ΟΡ ΙΧΕ

ΧΑΡΡΙΕΣ ΠΙΕΧΕΣ ΟΦ ΡΟΧΚΣ ΑΝ∆ ∆ΕΠΟΣΙΤΣ

Χ) ΣΕ∆ΙΜΕΝΤ: ΛΟΟΣΕ, ΦΡΑΓΜΕΝΤΕ∆ ΣΥΡΦΑΧΕ ΜΑΤΕΡΙΑΛ

II WEATHERING PROCESS:

Α ΜΕΧΗΑΝΙΧΑΛ ΩΕΑΤΗΕΡΙΝΓ (ΒΡΕΑΚΣ ΡΟΧΚΣ ΙΝΤΟ ΣΜΑΛΛΕΡ ΠΙΕΧΕΣ)

∀ • ΦΡΟΣΤ ΩΕ∆ΓΙΝΓ (ΕΞΠΑΝΣΙΟΝ ΟΦ ΧΡΑΧΚΣ ΙΝ ΡΟΧΚ ΑΣ ΩΑΤΕΡ ΙΝ ΤΗΕ ΧΡΑΧΚ ΦΡΕΕΖΕΣ ΑΝ∆ ΕΞΠΑΝ∆Σ)

OTHER MECHANICAL WEATHERING

– Removal of overlying rock allows

expansion and fracturing

• Plant growth

– Growing roots widen fractures

• Burrowing animals

• Thermal cycling

Mechanical Weathering

Mechanical weathering-contd.

Mechanical weathering-contd.

Surface Area & Weathering

Frost Wedging

CHEMICAL WEATHERING (LARGELY

pH Scale

Climate weathering

3.OXIDATION (REACTION OF CERTAIN CHEMICALS WITH O2)

Spheroidal weathering

FACTORS THAT INFLUENCE CHEMICAL

MINERAL COMPOSITION: RELATIONSHIP BETWEEN A MINERAL’S

TEMPERATURE AND PRESSURE OF CRYSTALLIZATION AND ITS

SUSCEPTIBILITY TO WEATHERING (HIGH TEMP LESS STABLE AND EASILY WEATHERED-EXAMPLE: OLIVINE &

CRYSTALLIZATION -PYROXENE)

THE EARTH’S SURFACE

Mineral composition

Rounded Boulder

D.SOME PRODUCTS OF CHEMICAL WEATHERING:

– O horizon - uppermost layer; organic material

– A horizon - dark layer rich in humus, organic acids

– E horizon - zone of leaching; fine-grained components removed by percolating water

– B horizon - zone of accumulation; clays and iron

oxides leached down from above

– A horizon - partially weathered bedrock

Bedrock composition on soil

Soils and Climate

• Soil thickness and composition are

greatly affected by climate

– Wet climates:

• More chemical weathering and thicker soils

• Soils in moderately wet climates tend to have significant clay-rich layers, which may be solid

– Arid climates:

• Less chemical weathering and thinner soils

• Subsurface evaporation leads to build-up of salts

• Calcite-rich accumulation zones may form,

– Extremely wet climates (e.g., tropical rainforest)

Vegetation and soil development

Typical Mature soil

Typical Mature Soil