198 TROCEEDINGS OF 



The soil of the hills, in the eastern part of Charlestown, abounds in fragments 

 of slate, of a coarse texture, with numerous specks of black mica, and sometimes 

 with small garnets, seemingly one of the varieties between argillaceous and mica 

 slate. These fragments are of all sizes — from a mere pebble to the weight of many 

 tons; some much worn, and others rough and angular, and with considerable dif. 

 ference in fineness of texture; They are all characterized, however, by the presence 

 of numerous crystals, of a curious character, which form the more immediate 

 objects of this paper, and of which I have the pleasure to send the National Insti. 

 tution a number of spechnens ; an end of each of which I have cut and slightly 

 polished, for the purpose of showing more readily the structure. 



These crystals have been variously denominated by different persons who have 

 seen them, though no one appears to have given any careful description of them. 

 One of the first persons who mentioned them to me, when I came into this part of 

 the country to live, spoke of them as being crystals of staurotide ; another after, 

 wards called them made, (and they are so termed in Cleveland's Mineralogy,) while 

 Dr. Jackson, in the last report of his geological survey of New-Hampshire, speaks 

 of them as maele, or (apparently as synonymous) hemitropic andalusite. They 

 are certainly of considerable variety of structure, under a general similarity of con- 

 figuration; and, while agreein'r exactly with none of the minerals described under 

 the foregoing names, have yet points of resemblance with each. 



Staurotide, or granatite, as called by some, belongs to the garnet family, and 

 made and andalusite are of the feld-spar flimily, if made be, as I presume, the 

 ■jamc as chiastolitc, according to the nomenclature of Jameson. His description of 

 the mineral, to which he gives this name, is, as far as my recollection serves, almost 

 precisely the same as that which Cleveland gives of made. 



The staurotide consists cf two si.t-sided prisms, intersecting each other either at 

 riffht angles or obliquely. The crystals in (question are sometimes found in this 

 form" and two of the specimens I send herewith, aftbrd instances of it — one being 

 an intersection nearly at right angles, and the other an oblique intersection, at about 

 forty-five degrees. The generality of the crystals are, however, single, consisting 

 of four-sidcd prisms, the bases of whidi are citb.cr rhomboids or rhombs. In tlio 

 most perfect crystals, the latter shape is the prevalent one, and the figure is often 

 verv exact, the angles being extremely well defined. Tlicy have also a natural 

 cleavage tlirough the shorter diagonal of the rhomb, by which they are divided into 

 two triangular prisms. Now llaiiy shows that the primitive form of granatite is a 

 quadrangular prism, the bases of which are rhombs, willi a similar cleavage through 

 the shorter diagonal of tho bafe. The angles of the rhombs he makes to be about 

 130° and .')0^, which agrees with tiic measurement of some of the most perfect of 

 these crystals. 



Some of them also agree with staurotide in otiier external cliaracters, as the 

 dark reddish, bro.va color, the internal glimmcriiig lustre between \ itreous and re- 

 sinous in the general cliaractcr of the fracture, in opacity, witii occasional trans, 

 luccncv, in hardness, briltleness, aud infusibility. Yet still the specimens, in which 

 these last characters are best marked, are precisely those which I have always 

 found single, with rhombic or rliomboidal bascE, and not intersecting eacli other. 

 Those so intersecting have a, dUrcrcnl set of cliaracters, apparently belonging more 

 to the description of made or chiastolitc, yet not precisely agreeing with that. 



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