John (Jack) H. Corbin
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B. Sc. Honours Thesis
STRUCTURAL STATE AND AL-SI ORDERING IN ALKALI FELDSPARS FROM THE LAKE GEORGE ADAMELLITE
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The Lake George Adamellite is a roughly oval body outcropping in Kings County, Nova Scotia. It is surrounded with biotite-granodiorite except the northwest corner where it is in contact with metasediments.
Single potassium feldspar crystal samples were separated from rocks collected from within and around the Lake George Adamellite. Unit cell parameters calculated by computer from x-ray powder diffraction charts were used to arrive at values for Al-Si ordering in the T1 sites by the method of Stewart and Wright (1974), using analysis developed by Kroll (1973).
Both orthoclases and rnicroclines analyzed were found to be highly ordered. One locality yielded significantly higher ordering values than all others. One of these crystals, a microcline, has probably arrived at its present state of order via an ordering process intermediate between the one-step and two-step ordering processes defined by Kroll (1973).
In several rocks analyzed, ordered microclines and orthoclases are found to coexist. Other researchers have reported similar findings (Steiger and Hart, 1967), ( Nilssen and Smithson, 1965).
More data wi11 be required if the precise causes of Al-Si ordering in the feldspars and the geological significance of the ordering are to be determined..
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Pages: 70
Supervisors: D.B. Clarke