MINERALOGICAL CHEMISTRY. Mineralogical Chemistry. ii. 107 Muscovite with Unusual Optical Characters from a Marble in Maryland. R. W. CLARK ailti W. F. Huw (Ceiztr. .lJi)? . 1915 666-668).--A greyish-brown dolomitic marble knowii in the trade as “Mar Villa” marble occurs in large quantity a t Cockeysville Maryland. It owes its colour to the presence of a brown mica which has the optical characters of phlogopite (markedly pleochroic; optic axial angle very small and optic axial plane parallel to the plane of symmetry) b u t the chemical composi- tion of muscovite (the ratio A1,0, SiO as shown in the follow- ing bulk analysis of the marble being nearer t o t h a t of muscovite 1 2 than to t h a t of phlogopite 1 6). SiO,. A1,0,,. FeO. CaO. MgO. MnO. CO,. FeS2. Total. 3.88 1.24 0.32 30.06 20.41 0.02 43.93 0.06 99-91” The percent age mineralogical composition calculated from this bulk analysis of the marble is dolomite (with MgO CaO = I 1-l) 93.97; muscovite 2-27; tremolite 3.75; pyrites 0.06. L. J. S.