First generation

Type I [pi. IS, fig. ]] Crystals of this type which occur in the
lining of a thin seam are characterized by the second order ]))-ramid
r (S.S.T5.3) developed to a considerable habit. This pyramid is terminated
by the rhombohedrons p. (lOTl) and £. (0112) all of which forms give excel-
lent reflections. The basal edges of the j)yramid are in some instances
truncated by narrow planes of the prism a (1120), the type gradually merg-
ing into the combination of type II shown in figure 2. The crystals, which
are for the most part colorless, transparent and brilliant, are very small,
the largest not exceeding 4 millimeters in length.
Type II [pi. IS, fig. 2-4]. Ci->'stals of t\-])e II are larger than those
of the preceding type, averaging 10 millimeters in vertical length. The>'



CALCITES OF NEW YORK I07

are pyramidal-scalenohedral in habit. The combination shown in figure
2 is essentially the same as that figured by Penfield and Ford in figure 1 of
their paper. This combination is characterized by the pyramid r (8.8.TB.3)
and the positive scalenohedrons K:(2l3l) and M:(7.4.TT.3) developed to
the extent of dominant forms. The prisms b (lOTO) and a (Il20) are
present as relatively small planes. The polar edges of r are truncated in
the positive sextants by narrow, brilliant planes of m. (405l), and the
polar edges of M : are beveled in the negative sextants by narrow,
somewhat roughened planes of tho negative scalenohedron 6 (1231). The
two beveling planes of this latter form were apparently assumed by
Penfield and Ford to correspond to the single plane of the rhombohedron
(0.12.T2.5) from which, however, they were unable to obtain satisfactory
reflections.
