LIME. 



mafs of brown iron-floiie ; and alfo in combination with the 

 planes of the primitive rhomboid and tholL' of Nos. i, 2, 3, 

 4, 1 1, and 36. The cryllals exhibiting this modification are, 

 with a few exceptions, ail from Derbylhire. 



20. ylcuU rhomboid of ^y ^^', and 12^ 26'.— This rhom- 

 boid, which has been obferved complete, and in combination 

 remains of the primitive planes, and thofe of Nos. 2 and 3, is of 

 ftill rarer occurrence than the preceding. Found in Derbylhire 

 and Cumberland. The preceding, and the next modiiication, 

 fometimcs exhibit, underneath"their pyramidal edges, the 

 planes of the priinitive rhomboid, which, elpcciahy when 

 of a diitcrent tint from the rell, are vifible througli the fub- 

 Itance of tlie cryftal ; a phenomenon produced by a fuper- 

 pofition of cryilalline matter on the cryllal already 

 formed. 



21. Acute flximbotd of ^o" ^A^ , and 1 29° 6'. — This occurs 

 both fimple and combined with other modifications, fuchas 

 Nos. I, 2, 3, 4, II, 17, and 46, in the Hartz, in Cumber- 

 land, and more frequently in Derbylhire. It is often feen to 

 accompany (lalaftitical varieties of calcareous Ipar. 



22. Very acute rhjmbohi of T^-j' 3 i', and 142 29' — This is 

 the chaux carb. ?7i:xtc of Hauy (pi. 23. lig. 6.) It is, like 

 the preceding, not unfreqnently met with, particularly as 

 accompanying ilaladtitical lime-ftone ; it occurs as often in 

 a complete (late as combined with the planes of other m.o- 



difications, amonsc which are Nos. 



'3>4. 



and 46. 



They are principally found in Derbylhire. Tlie variety 

 which is combined wdth the planes of No 4, has been de- 

 fcribed by Haiiy under the name of utilmixte (Ann. du 

 Iiluf. vol. i.) ; and that with the planes of No 1 1, and re- 

 mains of the primitive planes, is called by the fame cryftal- 

 lo'j-rapher chaux carb. tri-rhomhai(!a:e (Min. pi. 25. fig. 17.); 

 that with additional tr.ices of the planes of No. 7, is his 

 chaux carb. quadrl-rhomboidale (Ann. du Muf. vol. i.). When 

 the planes of this variety, and thofe of Nos. 11 and 3, are 

 united at the extremities of the prifmatic modification No. 2, 

 it is Haiiy's chaux carb. ar.ntilaire (ibid.) 



23. Extremely acute rhomboid of 14' 6', and l6j'' 54' This 



is the mod acute of all the rhomboids that belong to calca- 

 reous fpar. It is feldom feen in its complete Itate, both 

 on account of its minutenefs and its extreme fragility ; M. de 

 Bournon has, however, obferved it feveral times on the 

 groups of calcareous fpar from the Hartz, which are confider- 

 ed as filiform and indeterminable. The combination of the 

 planes of this with thofe of No. 4, is named ciiaux carb. 

 ddatee by Haiiy (pi. 24. fig. 31.}, which occurs alfo as 

 made ; that with traces of the planes of Nos. 3 and 17 is 

 the fame cryilaliographer's chaux carb. hyperaxide (pi. 25. 

 fig. ;o.) ; and that with Nos. 4 and 7, his chaux carb. rr/ro- 

 ^rade (pi. 26. fig. 36.) It occurs alfo with the planes of 

 feveral other modifications. This rhomboid might eafily be 

 miltaken for that of No. 13, v/hicii is, however, the refult of 

 quite a different decrement of the cryilalline laminx, aud con- 

 fequently has a different cleavage. 



III. Pyramidal Modif.calions. 



The feveral pyramidal dodecahedrons belonging to this di- 

 vifion, are here diilinguifned from each other by the mealure 

 of the fohd angle of their lummit, taken on two oppofite 

 edges of the pyr.nnid. 



A. Pyramidal obtufe dodecahedrons — The modifications of 

 this fub-divifion of pyramidal dodecahedrons are, upon the 

 whole, very rare, and almoft pccuhar to England, where they 

 occur in Derbylhire, Cumberland, and Durham. When the 

 planes of feveral of thofe modifications are combined in the 

 fame cryftal, theur narrownefs, together with the very obtufe 



3 



angles they form with one another, fometimcs produces curvi- 

 linear planes, efpecially when they are, at the fame time, com- 

 bined with the planes of feveral of tlie rhomboidal modifications. 



The following ten modifications, with the exception of 

 Nos. 27 and 30, have not been noticed before. 



24 Obtufe pyramidal dodecahedron of i'^^' 28'. — This modi- 

 fication (as well as thofe that follow), is the reiult of a retro- 

 gradation of the cryftalline laminx, along, and parallel with, 

 the edges of the pyramids of the primitive rhomboid, replacing 

 each of thefe edges by a double plane or bevelment. Three 

 of the edges in each pyramid of this modification muft, there- 

 fore, be exaftly in the fame direftion with thofe of the primi- 

 tive rhomboid. It has not been obferved either in its pallage 

 from the primitive rhomboid, or as complete dodecahedron, 

 but only in combination with very fhort planes of the prifm 

 No. 2 (from Cumberland) ; with thofe of Nos. 2, 4, and 

 36, in a pyramidal cryftal from Derbylhire ; and with thofe 

 of Nos. 2 and 3 j, from the fame county. 



23' . Obtufe pyramidal dodecahedron &/' i 26 ^ 5 1 '. — This modi- 

 fication, if it exiiled in a complete Hate, woidd exhibit py- 

 ramids with planes forming ifolceles triangles, and conle- 

 quently with all the angles of the common bafeon the fame 

 level. M. de Bournon has but twice obferved this modifica- 

 tion ; and in both cafes combined with the planes of leveral 

 othei' modifications, among which thofe of the prilm No. 2 

 are the moft apparent. From Derbyfliire. 



26. Obtufe pyramidal dodecahedron of 124' 36'. — This is 

 of much more frequent occurrence th;m the preceding, from 

 which it differs eflentially, in having fcalene triangles. The 

 complete dodecahedron comes from Derbylhire ; a combina- 

 tion of its planes with thofe of No. 2 from Cumberland. 

 In Derbyfliire it is alfo found combined with the planes of 

 feveral other modifications, of which thofe of Nos. 2 and 36 

 are the moft chaiaiSeriftic. 



27. Obtufe pyramidal dodecahedron of 121° 26'. — Theplanes 

 that terminate Haiiy's chaux cavh . Joti/lraffive ipl. 26.fig.37.) 

 belong to this modification. They are alio feen in his 

 chaux carh. furcompofee (pi. 28. fig. 50.), in w'hich five mo- 

 difications are combined. Cryltals with planes of this dode- 

 cahedron are common in Derbylhire and Cumberland, where 

 it occurs combined with the planes of feveral other mod;fi« 

 cations. The complete dodecahedron is Icarce. 



28. Obtufe pyramidal dodecahedron of 118" 26'. — Has not 

 yet been found in a complete llate. The fimpleft combina- 

 tion is that with the very Ihort planes of the prifmatic modi- , 

 fication No. 2. But it generally occurs together with the 

 planes of feveral other modifications, fuch as with Nos. 4, 

 7, II, 27, 28, and 36, and in lome of thefe alio, with re- 

 mains of the planes of the primitive rhomboid. Found prin- 

 cipally in Derbylhire and Cumberland. 



2 9. Cltufe pyramidal dodecahedron of 11 J 25 '. — Differs but 

 little from the preceding. It has not been found in a complete 

 ftate, nor are its planes often ftcn combined with thole of 

 other modifications j among thofe figured by M. de Bournon 

 are Nos. 2, 15, 17, and 36. The cryftals which exhibit its 

 planes are moftly from Derbylhire. 



30. Oblufe pyramidal dodecahedron of T 1 ^ 17'. — Its planes- 

 are reprefenled in Hauy's chaux carb. diijainte (pi. 26, 

 fig, 38.), in which it is combined' with thofe of Nos. 2 and 36. 

 In the fame author's chaux carb. bint^enaire (Ann. du Muf. 

 vol. i. ) it is feen without the planes of tlie prifmatic modif. 

 No. 2, but with thofe of No. 36 ; and his chaux carb. additive 

 (ibid.) is the bifonaire, augmented by the planes of No. 4. 

 Thefe cryftals are faid to come from Derbylhire. M. de 

 Bour'ion has not iiimfelf ftcn cryftals with planes of this 

 modification, 



51. Cltife 



