Leaching of Fluoride from Biotite Mica in Soil: Implications for Fluoride in Shallow Groundwater

Table 1

Physical and optical properties of biotite samples.

Sample	Weathering intensities	Appearance properties	Optical properties
M1	Highly weathered	Light brown color, highly disintegrated material.	About 50% of chlorite is present. Optical and physical properties of typical biotite grains are lacking.
M2	Moderately weathered	Light brown color, highly altered along cleavage.	Slightly disintegrated biotite crystals show pale yellow under the plane polarized light. About 25% of chlorite is present as interstratified alteration products.
M3	Moderately weathered	Black color. Less altered along cleavage.	Pale yellow under the plane-polarized light. Considerably large amount of pale green chlorite is present as patches along the cleavages and as interstratified alteration products.
M4	Moderately weathered	Black color. Slightly altered along grain boundary.	Pale green patches of chlorite present along the grain boundaries and basal surfaces are smooth, and cleavages are visible.
M5	Fresh	Dark greenish black color altered hexagonal plates.	No alterations within grains or along cleavages. The color under plane-polarized light varies between yellow, dark brown, and green. Yellow and brownish green pleochroism mottled appearance when the mineral is close to the extinction position. Free of inclusions.