Download Lithosphere is composed of elements i.e Si, Al, Fe Elements +

Lithosphere is composed of elements i.e Si,
Al, Fe
Elements + oxygen
SiO2
60.1
Al2O3
15.6
Fe2O3 3.4
FeO
3.9
MgO
3.5
CaO
5.1
Na2O
3.9
K2O
3.2
TiO2
1.0
oxides
Elements + oxides + compounds
minerals
Homogeneous solid
Characteristic chemical composition
Regular ordered structure (crystal)
Atomic ordering
Mineralogical Composition of Lithosphere
Carbonates (CO32- ) 9%
Silicate (SiO2) *
Feldspars
Quartz
Clay Minerals
Fe-Mg Silicates
39%
28%
18%
2%
*% of rock forming minerals
Combination of minerals
Rocks
Igneous
weathering
Sediments
transport
Metamorphic
diagenesis
Sedimentary rocks (66%)
Feldspars
(Alumina silicate Al2O3 – SiO2)
-K (orthoclase)
NaAlSi3O8
-Na / Ca (plagioclase)
Weathering involves mechanical, chemical and biological agents
Mechanical : abrasive forces caused by wind, water, temperature
Chemical : solution, hydrolysis, oxidation
2FeO + ½ O2 + H2O
2FeO(OH)
goethite
3(MgFeSiO4) + 2H2O
olivine
H4Mg3Si2O9 + SiO2 + 3FeO
serpentine
Biological : bacteria, roots (release of organic acids)
STRUCTURE
“Building Block”
Si + 4O
Si4+
Al+2O+4OH Al3+ O2-
Si: tetrahedral arrangement
Al: octahedral arrangement
hexagons
sheets
This structure is responsible for the clay properties
Theoretical formula
Al2O3 . 2SiO2 . 2H2O
39.4% 46.6% 13.9%
2:1 Mica
1:1 Kaolinite
Si
Al
Si
Al
Si
K+
Al
Si
Clay minerals
Rocks (quartz, carbonates etc)
Fe-oxides
Organic matter
<3
μm
-3
μm
65
>65 μm
THE CLAY / WATER SYSTEM
Plasticity is achieved when mixed with water
Nature of water which provides plasticity
•Interlayer lattice water
•Chemically combined water (hydroxyls)
•Absorbed by clay particles or weakly bound to surfaces an edges
Atomic structure of water resembles silica
Water molecules tend to join into
tetrahedrons which form hexagons in three
dimensional space
Ions can be trapped in the holes of the ring
Water ions immediately in contact “immobilized”
(“quasi-crystalline”). This area increases with charge
density of the ion.
Clays (kaolinite) has free Al3+ Si4+ at edges and O2- OH- on the sheets.
Clay particles act as an ion
Na-rich clays require less water than a Ca-rich clay
Si4+
O2- OHAl3+
Plasticity
Clay + Water → shape by pressure and retain
Parameters affecting plasticity
Particle size
Particle shape
Surface tension
Adsorbed ions
Organic content
Non plastic inclusions
Charge ↑ Size ↓ Plasticity↑
DRYING
Shrinkage
Leather-hard
Pore
Pore and
absorbed
Dry
CHANGES IN CLAYS DURING FIRING AND COOLING
100-200
470
400-600
450-550
300-800
400-650
580
500-800
750-850
800-850
850
900-950
1000
1050
1100
1150
Loss of absorbed water
Red glow can be seen
Loss of hydroxyl water
Loss hydrox water in kaolinite
Loss hydrox water in smectite
Oxidation of organic matter
Quartz inversion
NaCl, MgSO4, Na2CO3 migrate to surface
Dissociation of CaCO3 (CaCO3
CaO + CO2)
Chlorite disappears
Formation of Fe2O3 aggregates
Pyroxens (diopsite CaMg(CO3))
Illite disappears. Spinel forms.
CaO+clay
calcium silicates (wollastonite)
Calcium ferrosilicates formation
Light yellow heat
Mullite (Al2O3.2SiO2) forms
White heat in kiln
Raw Clay
950 re
950 ox
Non-Calcareous
Clay
1000 ox
1050 ox
1000 re
1050 re
Calcareous ceramic
High temperature Mineral development
Decoration of prehistoric ceramics
After drying and before firing
Black
Red
White
After firing
White Blue Green
Yellow
Black Decoration
Raw Materials
Compound
Carbon (soot)
Graphite
Mn minerals
(pyrolusite)
+ Fe-rich clay
Mn2O3
Mn3O4
MnFe2O4
Mn-spinels
Fine suspension
of Fe-rich clay
Fe3O4
FeAl2O4
γ-Fe2O3
Atmosphere
Reducing
Low temperature
Oxidizing or
Mild reducing
ReducingOxidizing
Mn-black technique
2MnO2 → Mn2O3 + 1/2O2 (485oC)
3Mn2O3 → Mn3O4 + 1/2O2 (870oC)
PO2↓ production at
lower temperatures
Phases formed during firing in oxidising atm.
Bixbyte Mn2O3
Haussmanite Mn3O4
Spinels MnOFe2O3 depending on the original
Mn/Fe ratio
Braunite 3Mn2O3 MnSiO3
Phases formed at intense reduction
Mn3Al2Si3O12 never detected
Mn-black technique
Mn-black technique
Neolithic Period - 3800 BC
Middle Bronze Age in Cyclades -1700 BC
Late Bronze Age Mainland -1600 BC
Black Decoration
Raw Materials
Compound
Carbon (soot)
Graphite
Mn minerals
(pyrolusite)
+ Fe-rich clay
Mn2O3
Mn3O4
MnFe2O4
Mn-spinels
Fine suspension
of Fe-rich clay
Fe3O4
FeAl2O4
γ-Fe2O3
Atmosphere
Reducing
Low temperature
Oxidizing or
Mild reducing
ReducingOxidizing
Fe-black technique
Clays rich in Fe (>5%) go dark in reduction due to Fe2+ phases
Fe2O3 → Fe3O4 → FeO → Fe
hematite magnetite
Fe-black technique
Ox 900-950 oC
Re 850-900 oC
Ox 800-850 oC
Fe-black technique
Red decoration (orange, purple)
Fe-rich clays fired in oxidising atmosphere → α-Fe2O3
Fe-red post-firing (Neolithic Period)
Franchthi, Peloponnese
Gioura, Sporades