GALLERY.] 
natural history. (Minerals.) 
55 
varieties of porphyry;—the labradorite feldspar (also called opalescent, 
feldspar, from its often exhibiting a beautiful play of colours in cut 
and polished specimens, of which a pretty complete suite is added), 
chiefly from the coast of Labrador and from the transition syenite 
of Laurwig in Norway * ;—together with some other species separated 
from orthoclase. To these is added the leucite or amphigene, chiefly 
from Vesuvius, in separate crystals of various sizes and degrees of 
transparency, massive, embedded in pyroxenic and other lavas. 
Case 31. Among other mineral substances here deposited, and 
partly belonging to the preceding section, are, the triphane or spodu - 
men and the petalite: in which latter substance lithia was first dis¬ 
covered by Arfvedson;—the davyne of Monticelli;—the nepheline, 
from Mount Vesuvius, with which are now combined several varieties 
of the elceolite or fettstein of Werner;—the wernerite , under which 
name, formerly confined to some varieties of common and compact 
scapolite, are now by most mineralogical writers united the meioniie 
of Vesuvius, and the greater part of the scapolite , the paranthine , the 
dipyre , the nuitallite , the bergmannite , the rosellite, and the amphodelite; 
substances which, together with several others provisionally placed in 
this Case, stand in need of further investigation as to their chemical 
and crystallographical characters. 
Case 32 contains chiefly micaceous and talcose substances. Our 
imperfect knowledge of the optical properties and chemical constitution 
of many varieties of the former, does not admit of their being arranged 
according to those distinctive characters; such varieties as have been 
more closely examined in this respect, may be divided into potassa-mica 
(by far the most common), which has two axes; magnesia-mica ( biotite 
of Hausmann), which has but one axis : in characteristic specimens 
from various localities, particularly from Vesuvius, where it occurs in 
small, but brilliant and transparent six-sided prismatic crystals; and 
lithia-mica , which besides the beautiful peach-blossom, red, violet, 
greenish-grey, and white scaly varieties knowm by the name of lepidolite, 
(some varieties of which, however, are referable to the silicates com¬ 
bined with fluorides, in Case 58 A,) from Rozna in Moravia, also 
comprises several large-foliated varieties of what w 7 as formerly con¬ 
sidered as common mica, such as that from Zinnwald in Bohemia 
and Altenberg, accompanied by apatite, tinstone, and topaz. 
The species and varieties of the talc-like substances are likewise very 
imperfectly understood. Among the specimens of talc in this Table 
Case, some varieties of which are chemically related to steatite, may 
be particularized the common or Venetian (which enters into the com¬ 
position of cosmetics), and the indurated talc; to the former of which 
was also formerly referred the green radiated talc from Siberia, com¬ 
posed of distinct groups of small diverging laminae, and which is knowm 
under the name of pyrophyllite; — potstone, ollite, or lavezzo (the 
lapis comensis of Pliny), which appears to be an intimate mixture of 
talc and asbest, chiefly from Chiavenna, near Como, where it is 
manufactured into culinary vessels;— chlorite , crystallized in ag¬ 
gregated, small, modified rhombic prisms : the earthy and foliated 
varieties, coating crystals of octahedral magnetic iron-stone, &c. 
Other related mineral substances are—the pennine; —the scarce leuch- 
* The top of the small octagonal table, standing near Case 30, is a slab of opales¬ 
cent feldspar from Finland. 
