(Fig. 1), as is well known, is constructed from a rhombohedron of. From Wordnik.com. [Scientific American Supplement, No. 441, June 14, 1884.] Reference
As in the other rhombohedral carbonates, the crystals possess perfect cleavages parallel to the faces of the rhombohedron. From Wordnik.com. [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 4 "Bulgaria" to "Calgary"] Reference
Its crystals have formed in a textbook rhodo shape--rhombohedron--very geometric, very distinct, with nice sharp, flat faces. From Wordnik.com. [In Pictures: Highlights Of Marc Weill's Mineral Collection] Reference
Distinct crystals are somewhat rare; they have the form of the primitive rhombohedron (rr '= 72° 20'), the faces of which are generally curved and rough. From Wordnik.com. [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 4 "Bulgaria" to "Calgary"] Reference
The end faces are cut off in such a manner that the angle of 72° which they originally form with the lateral edge of the rhombohedron is reduced to 68°. From Wordnik.com. [Scientific American Supplement, No. 441, June 14, 1884.] Reference
This lamellar twinning is of secondary origin; it may be readily produced artificially by pressure, for example, by pressing a knife into the edge of a cleavage rhombohedron. From Wordnik.com. [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 4 "Bulgaria" to "Calgary"] Reference
Depending on the habits of the crystals, certain trivial names have been used, such, for example, as dog-tooth-spar for the crystals of scalenohedral habit, so common in the Derbyshire lead mines and limestone caverns; nail-head-spar for crystals terminated by the obtuse rhombohedron. From Wordnik.com. [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 4 "Bulgaria" to "Calgary"] Reference
An important property of calcite is the great ease with which it may be cleaved in three directions; the three perfect cleavages are parallel to the faces of the primitive rhombohedron, and the angle between them was determined by W.H. Wollaston in 1812, with the aid of his newly invented reflective goniometer, to be 74° 55 '. From Wordnik.com. [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 4 "Bulgaria" to "Calgary"] Reference
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