L 1 M E. 



in i-ombination with thofc of Nos. I, 3, 5, 8, 41, and 43 j 

 molt of them from the Hartz. Perhaps fome of the very 

 flat lenticular varieties of calcareous fpar may be alfo referable 

 to this modilication. 



q. Sligkly ohtuji rhomboid of 95° 2ft', and 84' 32'.— This 

 very rare modilicHtion is produced by the obtufe anglrs on 

 the bafe of the primitive rhomboid being replaced, each by 

 a plane refting on the correfpondinir primitive planes. It is 

 obvious, that the cleavage of this rhomboid mail be different 

 from that of the hill mentioned modification, by being on 

 the planes of the fiimmit inltcad of the bafe; while that of 

 all the preceding rhsmboids, likewife at the bale, takes 

 T)lace on tlie edges. This rhomboid has been obfervcd per- 

 left in fpecimens from Siberia ; and in combination with 

 the planes of No. 36. 



B. Acute rhomboiiU. Nos. lo, 12, 15, 16 and iS — 21 of 

 this divilion are new. 



10. ylcute rhomboid of 6 J' 28', and 1 14° 32' The obtufe 



angles of t'.ie primitive rhomboid replaced each by a plane, 

 as in the preceding ; but being the refult of a more rapid 

 decrement of the lamina:, its axis is three times longer than 

 that of the primitive rhomboid. Occurs, though rarely, 

 in Dcrbyfhire, both in its complete ilate, and in combination 

 with remains of the planes of No. 2. 



1 1 . ylcute rhomboid of 45 '' 34', and 134° 26'. - The refult 

 of a decrement on the fame angles as in the preceding, but 

 the decrement prodiking a rhomboid much more acute. 

 It is the chaux carb. coiitrajiante of Haiiy (pi. 23. fig. 5.) 

 one of the moll common rhomboids that occur in calcareous 

 fpar. It occurs perfect, fomctimes with traces of the pri- 

 mitive planes, and in combination with Nos. i, 2, 3, 4, and 

 36. Is found in Derbvlhire, Cumberland, at Grenoble in 

 France, on the Hartz, &c. When the planes of the rhom- 

 boid of this modification are combined with thofe of the 

 common acute pyramidial dodecahedron, No. 36, they, re- 

 place the folid angles of the bafe of this dodecahedron in the 

 form of an elongated trapezoid. 



12. Acute rhomboid of ^o'^ 36', and 139- 34'. — Decrement 

 on the fame angles as in the preceding, to which it ap- 

 proaches clofely. Occurs mollly in its complete ilate in 

 Uerbylhire, and has been feen combined in the fame cryllal 

 with planes of the primitive rhomboid, and Nos. i, 14, and 

 36, in which latter its planes are placed nearly in the fame 

 manner as thofe of the rhomboid of the preceding modi- 

 fication. 



1 3. Very acute rhomboid of i j' and 165''. — Decrement on 

 the fame angles as in the preceding modifications, but giving 

 origin to a much more acute rhomboid. Count Bournon 

 has obferved it in its complete Hate. It is feldom feen, and 

 it is difficult to preferve it, on account of the great fragility 

 of the fine termination of the cryllals. Combinations of 

 the planes of this and No. 4 occur in Derbyfhire, on the 

 Hartz, &c. and in Cumberland, generally on cryllals of 

 fulphate of barytes ; the one called chaux carb. coniraSce 

 (Haiiy, pi. 24. fig. 20.) belongs to it. Fine groups of 

 this modification in its complete Hate have been found in 

 Wcftmoreland ; and in the lame fpccimen, combined with 

 planes of the very acute pyramidal dodecahedron, No. 54. 



14 Slightly acute rhomboid of ?)■]' ^2' , and g2^ 18'. — This 

 is the chaux carb. cuhdide of Hauy, (pi. 23. fig. 7.) It 

 occurs complete, with planes of the primitive rhomboid, and 

 combined with the planes of fevcral other modification'', 

 fuch as Nos. 1 — 4, and No. 15, in Languedoc, at Stron- 

 tian, Bi»th, in Derbylhire, and on the Hartz. This modifica- 

 tion," combi:!ed with the planes of No. 3, is the chaux 

 carb. apoph'ine oiWixx)-, (pi. 24. fig. 15.) 



15. Acute rhomboid c/84" 26', and g^" 34'. — This rhom- 



boid, the preceding, and all the following, arc the refult 

 of a decrement of the cryftalline laminae on the obtufe 



angles of the.bafc ; and the cleavage in all of them takes 

 place at the fummit, and on the edges of the cryllal. Though 

 combined with moll of the other modifications, the planes 

 of this rhomboid have never been mentioned by cryllallo- 

 graphers, a circumllance probably owing to their fmallncfs, 

 and tlieir having been confounded with the preceding, from 

 which it is, however, cafily dillinguilhed, even without the 

 alfidance of the goniometer. It is fometimes found in a 

 complete ftate on the Hartz, and at Strontian in groups, 

 accompanied with ililbitc and crofs-ftonc, or harmoiomc, 

 and in combination with the planes of Nos. i — j. and alfo 

 with the remains of thofe of the primitive rhom.boid. 



16. Acute rhomboid of Si^ 19', rtni-/ 98^ 41'. — This is 

 oftcncr feen in its complete Ilate than combined witl; the 

 planes of other modifications, fuch as thofe of Nos. i, 2, 

 3, 4, and 36 ; it alfo occurs with traces of the primitive 

 rhomboid. Moll of thcfe were brought from the ifland of 

 Ferroe, and from Scotland ; the former mollly in groups, 

 with flilbite zeolite, the others with analcime zeolite. The 

 variety in which it is combined with No. 4, came from Caf- 

 tagna-moro, in Italy. Their gangue, in the above places, 

 is a wacke like rock. 



17. Acute rhomboid of y ^^ 31', and 104' 29'. — This is 

 the chaux carb. invcrfe (Haviy, pi. 23. fig. 3.), fo called 

 becauie this rhomboid is, as it were, an inverfion of the pri- 

 mitive. Next to No. 14, it is the moll common of all the 

 modifications of calcareous fpar ; but a circumllance worth 

 remarking is, that it fcarcely ever occurs in any other but 

 (liell liine-ftone ; while the reverfe prevails with regard to 

 the primitive rhomboid which, in its pcrfcft Hate, is feldom 

 found in any brt the older formations of lime-flone. The 

 name of muriatique, given to this rhomboid by Ronre de 

 I'Ifle, is derived from the juil mentioned mode of oc- 

 curing. The complete rhomboid frequently occurs in 

 veins at Bath, in Derbyfiiire, and lining hollows of (liell- 

 marble in feveral other parts of Britain. In dill greater 

 perfcftion it is found, together with various combinations of 

 the phines of other modifications, in the (hell lime-ftone of 

 Coulon, near Lyons, and in thofe ofVougy, near Roanne, 

 in Forez ; in the former of thefe places it is generally feen in 

 the interior of filiceo-calcareous geodes ; in the latter in 

 geodes of black, earthy, and compacl black manganefe, 

 with mammillary internal furface. It has been obferved by 

 M. de Bournon combined with the planes of the primitive 

 rhomboid, and with thofe of Nos. i to 4, and Ncs. 11, 14, 

 36, 37, and 49. That with narrow remains of the primitive 

 planes is Haiiy 's chaux carb. an//a(V« (pi. 23. fig-9-)> '''^t 

 with remains of the primitive planes, and ihofe of the prifm 

 No. 2, has been defcribed by the fame cryflallograjiher 

 under the name of chaux carb. uniiinaire (Ann. du iVIuf. 

 Par, vol. i.) ; that w>lh the planes of the fame prifm No. 2, 

 and with thofe of No. 3, is Haiiy's chaux carb. perfiflanta 

 (pi. 25. fig. 29.) ; the fame with additional remains of 

 the planes of No. 4, is his chaux carb. coardonnee ; and 

 a variety in which this rhomboid is combined with narrow/ 

 planci of Nos. 1, 2, 3, 4, and 37, is defcribed by hira. 

 under the name of chaux carb. quadruplante. (An». du 

 Muf. vol. i.) 



1 8. Acute rhomboid of 70° 1 8', and IC9" 42'. — This rhom- 

 boid is very rare, ana has been feen in combination only 

 with the planes of the prifm No. 2, accornpanied by planes 

 of Nos. 23, 30, 36, and of the primitive rhomboid. Thefe 

 cryllals occur in Cum.berland and in Derbyfiiire. 



19. Acute rhomboid of bl 12, a;«/iiS 48'. This has 

 been obferved by count Bournon, in its complete Ilate, im 2 



m-dfs 



