ALABAMA MICA DEPOSITS 29 



ting is then easy, because the cleavage of mica is so per- 

 fect and the tangled outside edges of the sheet have been 

 removed. By grinding a wedge edge on the sheets and 

 using a thin sharp knife, mica can be readily split into 

 sheets as thin as one-thousandth of an inch or thinner. 



As classified by physical peculiarities of crystalline 

 structure, color, and inclusions, mica is commonly known 

 to and spoken of by mica miners as "ruled" or "ribbon," 

 "wedge," "A-form," "hair-lined," "fish bone," and "tan- 

 gle-sheet." "Specked" or "clay-stained" mica, refers to 

 mineral or clay inclusions in closed or open books. "Rul- 

 ed" or "ribbon" mica, is formed by sharp parting planes 

 cutting through the mica crystals at an approximate an- 

 gle of 60 degrees with the base or cleavage surface, ex- 

 tending either through, or partially through, the crystal. 



Ruling lines however usually occur in closely parallel 

 formation, and while dividing the crystals into smaller, 

 inconveniently shaped and less valuable and recoverable 

 sizes, the grade of mica constituting the ruled portions, is 

 quite uniformly good, constituting the best part of the 

 crystal. No deposits of mica of any magnitude in the 

 State have been examined which do not show ruled mica 

 to greater or less degree, and in certain deposits it may 

 be said to predominate. The physical term "wedge" mica, 

 is of obvious meaning and refers to masses of varying 

 thickness on the edges, due to unequal crystalline devel- 

 opment. 



A-form, or A-structure mica, called by miners "horse- 

 tail," carries a double series of lines or striations form- 

 ing with each other an approximate angle of 60 degrees, 

 from which characteristic its name is derived. 



In "fish-bone" or "herring-bone" structures so-called, 

 the striations form with each other an approximate an- 

 gle of 120 degrees, meeting along the center line of the 

 crystal. 



"Tangle-sheet" is the trade and mining term used to 

 describe mica in which the laminae are so formed as to 

 split properly only in certain portions of the block, mainly 

 around the edges. "Specked" mica contains inclusions of 

 iron oxide or of other minerals with consequent reduc- 

 tion in grade and value. It is not of general occurrence 



