F 4.18 2.90. Li 4.85. biotite.
"The Student's Elements of Geology"
Sir Charles Lyell
W 0.44 2.70. biotite.
"The Student's Elements of Geology"
Sir Charles Lyell
In certain minerals, notably the brown variety of mica known as biotite, the microscope reveals minute circular marks occurring here and there, quite irregularly.
"The Birth-Time of the World and Other Scientific Essays"
J. (John) Joly