9
2.3. Results and Discussion
2.3.1. General Characteristics of Silicate Rocks
The total elemental and mineral compositions of the silicate rocks T0 are presented in Table 2.1. The total content of elements for each rock milled for
different time and condition is presented in Appendix A1, which values are used as the basis for calculating the proportion of extractable or dissolved elements i.e.,
of total in rock throughout the thesis. Table 2.1. Total elemental and mineral compositions of the silicate rocks at their
initial condition T0
Element
a
oxides Rock
SiO
2
Al
2
O
3
Fe
2
O
3 b
CaO MgO K
2
O Na
2
O TiO
2
MnO P
2
O
3
SO
3
Total
c
Basalt Dolerite
Gneiss K-feldspar
47.95 49.92
74.01 61.53
19.15 13.94
15.02 19.05
11.25 15.22
2.64 0.02
11.11 11.37
2.01 0.05
6.08 6.32
0.74 0.01
0.18 0.37
1.09 11.56
2.10 1.21
4.06 2.51
1.76 1.89
0.31 0.05
0.16 0.21
0.02 0.01
0.19 0.13
0.08 0.22
0.05 0.12
0.01 0.01
100 100
100 100
Basalt Dolerite
Gneiss K-feldspar
Mineral Composition
d
: Mg-Hornblende 5 - 6, Pargasite 5 - 6, Augite 5 - 6, Albite 6 - 6.5, Anorthite 6 - 6.5, Biotite 2.5 - 3, Phlogopite 2 - 2.5
: Mg-Hornblende, Pargasite, Augite, Albite, Anorthite, Biotite, Diopside 5.5 – 6.5
: Quartz 7, Albite, Biotite, Chlorite 2 – 3 : Microcline 6 – 6.5, Albite, Anorthite
a
Average values of 4 replicates.
b
Total iron is expressed as Fe
2
O
3
, much Fe is present as Fe
+2
.
c
Normalized to total of 100 to exclude structural H
2
O.
d
Duplicate measurements, and minerals listed in order of decreasing abundance, followed by relative hardness numbers Deer et al. 1992.
As shown in Table 2.1, mafic basalt and dolerite and felsic gneiss and K- feldspar rocks have quite different elemental and mineral compositions and contain
minerals of various relative hardness values. These differences may relate to their suitability for use as fertilizers and their responses to milling treatments.
The mafic rocks have similar elemental and mineral compositions, which are dominated by ferromagnesian silicates hornblende, pargasite, and augite of the
amphibole group. The total contents of silica are 47 - 50 SiO
2
and alumina are 14 – 20 Al
2
O
3
, with several macronutrient elements present in relatively large
10 amounts Ca 11 CaO and Mg 6 MgO. The hardness of most minerals present
in the mafic rocks is 5 – 6. The felsic rocks have different elemental and mineralogical compositions to
the mafic rocks. Gneiss is dominated by quartz with some feldspars and micas, whereas the K-feldspar is reported by Commercial Minerals Ltd. 1997 to consist of
microcline 65.6 , albite 31.2 , and anorthite 0.6 with minor kaolinite and free quartz. Both felsic rocks contain high concentrations of silica 61 - 75 SiO
2
and alumina 15 – 19 Al
2
O
3
, the major plant nutrients are K and Na. The concentration of K in K-feldspar 11.5 K
2
O is much larger than that for gneiss 1 K
2
O, conversely the concentration of Na in K-feldspar 2.5 Na
2
O is lower than that in gneiss 4 Na
2
O. Appreciable amount of Ca and Mg occur in minor mafic minerals in gneiss. The relative hardness of most minerals composing these
felsic rocks is 6 – 6.5. Based on their major plant nutrient contents, the mafic rocks could be
potential sources of Ca and Mg, and the felsic rocks potential sources of K providing that these elements are released to soil solution. An evaluation of these milled SRFs
is needed to identify the solubility of nutrient elements in soils.
2.3.2. Effects of Milling Time and Condition 2.3.2.1. Physical and Mineralogical Properties
Kategori