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 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)
∀ • ΣΑΛΤ ΧΡΨΣΤΑΛ ΓΡΟΩΤΗ (ΦΟΡΧΕΣ ΧΡΑΧΚ’Σ ΩΑΛΛΣ ΦΑΡΤΗΕΡ
ΑΠΑΡΤ)
∀ • ΤΗΕΡΜΑΛ ΕΞΠΑΝΣΙΟΝ ΑΝ∆ ΧΟΝΤΡΑΧΤΙΟΝ (ΑΛΤΕΡΝΑΤΕ
ΕΝΛΑΡΓΕΜΕΝΤ ΑΝ∆ ΣΗΡΙΝΚΙΝΓ)
∀ • ΜΕΧΗΑΝΙΧΑΛ ΕΞΦΟΛΙΑΤΙΟΝ (ΦΡΑΧΤΥΡΙΝΓ ΑΝ∆ ΡΕΜΟςΑΛ
ΟΦ ΣΥΧΧΕΣΣΙςΕ ΡΟΧΚ ΛΑΨΕΡΣ ΑΣ ∆ΕΕΠ ΡΟΧΚΣ ΕΞΠΑΝ∆
Υ ΠΩΑΡ∆ ΑΦΤΕΡ ΟςΕΡΛΨΙΝΓ ΡΟΧΚΣ ΗΑςΕ ΕΡΟ∆Ε∆ ΑΩΑΨ)

OTHER MECHANICAL WEATHERING
PROCESSES

GROWTH OF PLANT ROOTS (EXPANDS EXISTING CRACKS
IN ROCKS)
o
BURROWING ANIMAL ACTIVITIES
o
ABRASION OF TRANSPORTED PARTICLES
o


Mechanical Weathering
• Frost action
– Mechanic effect of freezing (and expanding)
water on rocks

• Pressure release
– Removal of overlying rock allows
expansion and fracturing

• Plant growth
– Growing roots widen fractures

• Burrowing animals
• Thermal cycling
– Large temperature changes fracture rocks
by repeated expansion and contraction

Mechanical Weathering


Mechanical weathering-contd.


Mechanical weathering-contd.


Surface Area & Weathering


Frost Wedging


CHEMICAL WEATHERING (LARGELY
CONTROLLED BY CLIMATE)
∗ΡΟΛΕ ΟΦ ΩΑΤΕΡ
∗∆ΙΣΣΟΛΥΤΙΟΝ
1. ΩΑΤΕΡ ∆ΙΣΣΟΛςΕΣ ΗΑΛΙΤΕ ΑΝ∆ ΓΨΠΣΥΜ
2. ΧΑΡΒΟΝΙΧ ΑΧΙ∆ ∆ΙΣΣΟΛςΕΣ ΛΙΜΕΣΤΟΝΕ
(ΧΟ2+Η2Ο−−−−ΗΧΟ3)
ι.
ΧΑΛΧΙΥΜ ΧΨΧΛΕ
ιι.
ΑΧΙ∆ ΡΑΙΝ


pH Scale

Climate weathering


3.OXIDATION (REACTION OF CERTAIN CHEMICALS WITH O2)
ι.
ιι.

ΙΡΟΝ ΟΞΙ∆ΕΣ
ΧΟΠΠΕΡ ΟΞΙ∆ΕΣ

4. ΗΨ∆ΡΟΛΨΣΙΣ (ΡΕΠΛΑΧΕΜΕΝΤ ΟΦ ΜΑϑΟΡ ΠΟΣΙΤΙςΕ ΙΟΝΣ
ΩΙΤΗ ΠΡΟΤΟΝΣ) ΟΦ ΠΟΤΑΣΣΙΥΜ ΦΕΛ∆ΣΠΑΡ ΙΝΤΟ
ι) ΧΛΑΨ: ΒΕΧΟΜΕΣ ΠΑΡΤ ΟΦ ΣΟΙΛ
ιι) ΣΙΛΙΧΙΧ ΑΧΙ∆: ΧΕΜΕΝΤΣ ΣΕ∆ΙΜΕΝΤΣ ΟΡ ΦΟΡΜΣ
ΑΝΙΜΑΛ ΣΗΕΛΛΣ ΑΝ∆ ΣΚΕΛΕΤΟΝΣ
ιιι) ΠΟΤΑΣΣΙΥΜ ΙΟΝΣ: ΠΡΟςΙ∆Ε ΠΛΑΝΤ ΝΥΤΡΙΕΝΤΣ


Spheroidal weathering


FACTORS THAT INFLUENCE CHEMICAL
WEATHERING
1.ΧΛΙΜΑΤΕ
ι) ΜΟΙΣΤΥΡΕ
ιι)

ΗΕΑΤ

ιιι) ςΕΓΕΤΑΤΙΟΝ
2. ΛΙςΙΝΓ ΟΡΓΑΝΙΣΜΣ
3. ΤΙΜΕ


Mineral composition
MINERAL COMPOSITION: RELATIONSHIP BETWEEN A MINERAL’S
TEMPERATURE AND PRESSURE OF CRYSTALLIZATION AND ITS
SUSCEPTIBILITY TO WEATHERING (HIGH TEMP CRYSTALLIZATION----LESS STABLE AND EASILY WEATHERED-EXAMPLE: OLIVINE &
PYROXENE)
REGOLITH: LOOSE, FRAGMENTED MATERIAL THAT COVERS MUCH OF
THE EARTH’S SURFACE
SOIL: UPPERMOST ORGANIC-RICH PORTION OF THE REGOLITH


Rounded Boulder


D.SOME PRODUCTS OF CHEMICAL WEATHERING:
a) CLAY MINERAL
i) KAOLINITE
ii) SMECTITE
iii) PRACTICAL USES FOR CLAYS
b) METAL ORES
i)

FORMATION OF BAUXITE

ii)

OTHER ORES


Soil
• Soil - a layer of weathered, unconsolidated
material on top of bedrock
– Common soil constituents:
•
•
•
•

Clay minerals
Quartz
Water
Organic matter

• Soil horizons
– 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
enough to form a hardpan

– Arid climates:
• Less chemical weathering and thinner soils
• Subsurface evaporation leads to build-up of salts
• Calcite-rich accumulation zones may form,
cementing soil together into a hardpan

– Extremely wet climates (e.g., tropical rainforest)
• Highly leached and unproductive soils (laterites)
• Most nutrients come from thick O/A horizons


Vegetation and soil development


Typical Mature soil