670 REPORT OF NATIONAL MUSEUM, 1897. 



Combination of a rhombohedron and a scalenohedron : Hematite, Elba (Cat. No. 

 82419, U.S.N.M.) ; calcite, England. (CJat. No. 83376, U.S.N.M.) 



Combination of a scalcnohedroii and a rhombohedron : Calcite, Jojjlin, Missouri. 

 (Cat. No. 84100, U.S.N.M.) 



Combination of a ^irism, rhombohedron, and a scalenohedron : Calcite, Higrigg mine, 

 Egremout, Englaud. (Cat. No. 51228, U.S.N.M.) 



Orthorhombic .system. — Axes unequal. All forms referable to three 

 axes of unequal length intersecting at angles of 90 degrees. 



Jixamj)les. 



The pyramid: Cerussite, Mies, Bohemia (Cat. No. 84117, U.S.N.M.) ; sulphur, Trns- 

 kanieCjGalicia, Hungary (Cat. No. 47270, U.S.N.M.) ; brookite, Magnet Cove, Arkansas 

 (Cat. No. 814G2, U.S.N.M.). 



The prism: Andalusite, Swarthmore, Delaware County, Pennsylvania (Cat. No. 

 81962, U.S.N.M.) ; staurolite, Li.sbou, New Hampshire. (Cat. No. 81901, U.S.N.M.) 



Combination of a prism, two domes, and the base: Celestite, Girgenti, Sicily. (Cat. 

 No. 84120, U.S.N.M.) 



Combination of a priam, pyramid, and the base: Chalcocitc, Kedruth, Cornwall, 

 England. (Cat. No. 84119, U.S.N.M.) 



Monoclinic system. — Axes une(iual. All forms referable to three axes 

 of unequal length. One axial intersection oblique, the other two at 

 angles of 90 degrees. 



Examples. 



The pyramid: Lazulite, Craves Mountain, Georgia (Cat. No. 45720, U.S.N.M.) ; tin- 

 kal. Fish Lake, Nevada (Cat. No. 7058, U.S.N.M.). 



The prism : Adularia, St. Gothard, Switzerland (Cat. No. 81932, U.S.N.M.) ; titanite. 

 New York (Cat. No. 83201, U.S.N.M.). 



Combination of a dotne and two prisms : Wolframite, Ziunwald, Saxony. (Cat. No. 

 84121, U.S.N.M.) 



Combination of the base, pinacoid, prism, and dome: Orthoclase, Breckenridge, Colo- 

 rado. (Cat. No. 13878, U.S.N.M.) 



Combination of the jjrism, pyramid, and two pinacoids: Pyroxene, iJiana, Lewis 

 County, New York. (Cat. No. 82496, U.S.N.M.) 



Combination of a pinacoid, pyramid, and prism : Gypsum, Ellsworth, Mahoning 

 County, Ohio. (Cat. No. 82.561, U.S.N.M.) 



Combination of two pinacoids, two pyramids, a prism, and the base: Diopside, Dekalb, 

 New York. (Cat. No. 48296, U.S.N.M.) 



Combination of a 2)rism, dome, pinacoid, and base : Heulandite, Beru-tiord, Iceland. 

 (Cat. No. 84157, U.S.N.M.) 



TricUuie system. — Axes unequal. All forms referable to three axes 

 of unequal length, and whose axial intersections are all oblique. 



Examples. 



The prism : Kyanite, Yancey County, North Carolina. (Cat. No. 83520, U.S.N.M.) 

 Combination of the base, pinacoid, prism, and dome: Albite, Macomb, St. Lawrence 



County, Now York (Cat. No. 81981, U.S.N.M.) ; oligoclase. Fine, St. Lawrence County, 



New York. (Cat. No. 48307, U.S.N.M.) 



SYMMETRY. 



A crystal shows symmetry when it can be revolved about an axis an 

 even multiple of 360 degrees without its position as a whole in space 

 being changed, or can be cut in halves which are to each other as their 



