168 



ALUMINA. 



^y 



HARMOTOME. 



Trimetric. In modified rectangular prisms ; and very 

 .^v. commonly twin crystals similar to the annexed 



/^\W\ figure * 



Color white ; sometimes grayish, yellowish, 

 or brownish. Subtransparent to translucent. 

 Luster vitreous. H=4- — 4*5. Brittle. Gr=* 

 2-39—2-5. 



Composition : silica 44*0, alumina 16*6, ba- 

 ryta 24*8, water 14*6. Fuses without intumes- 

 ence to a clear globule. Phosphoresces with a yellow light 

 when heated. Scarcely attacked by the acids unless they 

 are heated. 



Dif. Its twin crystals, when distinct, cannot be mistaken 

 for any other species except phillipsite. It is much more 

 fusible than glassy feldspar or scapolite ; it does not gelati- 

 nize in cold acids like thomsonite. 



Obs. Occurs in amygdaloid, gneiss, and metalliferous 

 veins. Fine crystallizations are found at Strontian in Ar- 

 gyleshire, Andreasberg in the Hartz, and Kongsberg in 

 Norway. 



The name harmotome is from the Greek harmos a joint, 

 and temno to cleave. 



Phillipsite. Near harmotome in its cruciform crystals and other 

 characters ; but differing in containing lime in place of baryta. It dif- 

 fers also in gelatinizing with acids and in fusing with some intumes- 

 cence. It also occurs in sheaf-like aggregations and in radiated crys- 

 tallizations. From the Giant's Causeway, Capo di Bove, and Vesuvius. 

 Zeagonite, from the last two localities mentioned, is identical witb 

 Phillipsite. 



ANALCIME. 



Monometric. Occurs usually in trapezohedrons, (fig. 1,) 

 1 also fig. 2 ; cleavage cubic and 2 



only in traces. 



Often colorless and transparent, 

 also milk-white, grayish and red- 

 dish-white, and sometimes opaque. 

 The appearance sometimes seen 

 in polarized light is shown in figure 96, page 61. 

 Luster vitreous. H = 5— 5-5. Gr=2'07— 2-28. 



What is the common form of harmotome 1 what its color and ap- 

 pearance 1 What are its distinguishing characters? What is the form 

 of crystals of analcime ? the color and other characters ? 



