MINERALOGY. 



6. Plenitude or Fulness of ike Crystals. 



453 



Plenitude 

 or fuloca 

 of thecrrs- 

 ttl. 



A. Full, as in almost all crystals. 



U. Excavated at the extremities, as in green-lead ore. 



C. Hollaai. Olive-green-coloured calcareous spar 



from Scbemnitz in Hungary, occurs in acute 



hollow three-sided pyramids. 



II. THE ALTERATIONS ON THE FUNDAMENTAL 

 FIGURE. 



Th alter*. These are produced by, 1. Truncation; 2. Bevel- 

 nont oo the ment ; 3. domination ; and, 4. Division of the Planet. 

 fundament- 

 al figure. 1. Truncation. 

 Truncation When we observe on a fundamental figure, in place 



of an edge or angle, a small plane, such a plane is 



denominated a Truncation. 



These new planes are named Truncating Planes, and 



the edges which they form with the other planes 



Truncating Edges. 

 We have here to observe what relates to the situation, 



magnitude, the setting on or position, and the direction 



of the truncation. 



a. In regard to the situation of the truncation, it is 

 either on the edges or on the angles, and sometimes 

 a few, sometimes all the angles and edges of the 



PIATH figure are truncated. Fig. 21. a cube truncated on 



CCCICTI. tn e angles ; and Fig. 82. cube truncated on the 

 r 'f- dg. 



b. In regard to the magnitude of the truncation, it is 

 either Jeep or slight, according as more or less of the 

 fundamental figure is wanting ; and consequently 

 the truncating planes are proportionally greater or 

 smaller. 



c. The planes are set on either straight or oblique. 

 They are said to be set on straight, when they are 

 equally inclined on all the adjacent planes ; and set 

 on cblitfufh/, when they are not equally inclined on 

 the adjacent planes. 



d. The truncating planes in regard to their direction, 

 are either straight or curved. In the latter case, we 

 also say that the edge or angle is rounded off. 



2. Bevelmenl or Cuneature. 



Bcrclment When the edges, terminal planes, or angles, of a 

 or cunra- fundamental figure are so altered, that we observe in 

 their place two smaller converging planes, terminating 

 in an edge, they are said to be bevelled. These two 

 newer or additional planes are named bevelling planet ; 

 and the edge formed by their meeting, the bevelling 

 edge. We nave here, again, to observe the situation, 

 magnitude, angle, uniformity, and setting on of the be- 

 en t. 



a. In regard to situation, the bcvelment is generally on 

 the edges, sometimes on the terminal planes, and 



ftg. w, 4, neldomer on the angles. Fig. 23. is a cube bevelled 

 *. M, >r! on the edges ; Fig. 24. a three-sided prism, bevel- 

 led on the lateral edges ; Fig. 25. a four-tided prism, 

 bevelled on the terminal planes, the bevelling planes 

 set on the lateral edges ; Fig. 26. a table bevelled 

 on the terminal planes; and Fig. 27. an octahedron 

 bevelled on all the angles. 



b. In regard to magnitude of the bevelment, it is either 

 deep or slight, according as more or less of the funda- 

 mental figure is wanting. 



c. In regard to the angle, the bcvelment is obtuse orjlal, 

 or rectangular or acute angular. 



d. The bevelment, in regard to uniformity, is either 

 unbroken, when it extends in one direction ; or 



broken, when each bevelling plane consists of several Oryetognu- 

 planes ; sometimes of two planes, when it is said to / 

 be once broken ; and sometimes of three planes, when '"""n" 1 "- 1 

 it is said to be tnicr broken. 



e. In regard to the setting on, we have to attend to the 

 position and the direction of the bevelling planes. 



a. In regard to the position, the bevelling planes are 

 either on planes or on edges. 



b. The direction varies only when the bevelling planes 

 are set on the terminal planes. It is said to be set 

 on straight when the bevelling edge is at right 

 angles to the axis of the crystal; and set on oblique, 

 when it forms an oblique angle with the axis of the 

 crystal. 



3. Acuminalion. 



A fundamental figure is said to be acuminated when, Acumina- 

 in place of its angles or terminal planes, we find at tion. 

 least three additional planes which converge into a 

 point, and sometimes, but more rarely, terminate in an 

 edge. 



We have here to observe the parts of the acumina- 

 tion ; these ar,e, 



The acuminating planes. 



The edges of the acuminalion, which are, 



The proper acuminating edges, those formed by 



the meeting of acuminating planes. 

 The edges which the acuminating planes make with 



the lateral planes of the fundamental figure. 

 The terminal edges of the acumination, which are 

 formed by the terminating of the acuminating 

 planes in an edge or line. 

 The angles of the acumination ; which are, 

 The angles which the acuminating planes form with 



the lateral planes ; and, 

 The summit angle. 



We have to determine in the acumination, its situation, 

 the number of its planes ; proportional magnitude of the 

 planet among themselves ; tne letting on or application of 

 the planes ; the angles of the acumination ; its magnitude 

 and termination. 



a. Its situation is either on angles, as in Fig. 28. and PLATE 

 29. or on terminal planes, as in Fig. 30. cccxcvi. 



b. The number oj planes is three, as in Fig. 33. and 34. ; F 'g- *6, 29. 

 four, as in Fig. 30. ; six, as in Fig. 31. ; or eight, as 30< " ** 

 in Fig. 35. 33 ' 34 ' '* 



c. The proportional magnitude of the planet among them- 

 stive i, is character of but little importance. They 

 are generally determinate!} 1 unequal, as in heavy- 

 spar; or undeterminately unequal, as in rock-crys- 

 tal. 



d. The setting on or application of the jjanei refers to 

 their position on edges, as in Fig. 9. 32. 34., or 

 planes, as in Fig. 28. 30. 31. and 33. When the 

 planes of an acumination are not set on all the edges 

 or planes of the fundamental figure, but only on the 

 alternate planes or edges, it is said to be set on alter- 

 naiely, as in Fig. 33. and 34. and when the acumi- 

 nating planes on both extremities of the fundamental 

 figure are set on the same planes or edges, it is said 

 to be conformable (rechtsinnig,) as in Fig. 31.; 

 but when the planes on opposite ends of the figure 

 are set on different planes or edges, it is said to 

 be uncnnformaile, as in Fig. 33. and 34. The 

 same expressions are applied to alternate Trunca- 

 tions. 



e. The angle of the acuminalion, or the summit angle, is 

 either obtuse or flat, as in garnet ; rectangular, as in 

 zircon ; or acute, as in calcareous-spar. 



