60 CRYSTALLOGRAPHY. 
3. Consisting of scales or lamelle. 
a. Plumose, having a divergent arrangement of scales, as 
seen on a surface of fracture; e. g., plumose mica. 
b. Lamellar, tabular, consisting of flat lamellar crystalline in- 
dividuals, superimposed and adhering. 
Micaceous, having a thin fissile character, due to the aggre. 
gation of scales of a mineral which, like mica, has eminent 
cleavage. 
d. Septate, consisting of openly-spaced intersecting tabular 
individuals ; also divided into polygonal portions by reticulat- 
ing veins or plates. A septariwm is a concretion, usually flat- 
tened spheroidal in shape, the solid interior of which is inter- 
sected by partitions; these partitions are the fiilings of cracks 
in the interior that were due to contraction on drying. When 
the surface of such septate concretions has been worn off, they 
often have the appearance of a turtle’s back, and are sometimes 
taken for petrified turtles. 
4. Consisting of grains. Granular structure. A massive 
mineral may be coarsely granular or finely granular, as in 
varieties of marble, granular quartz, etc. It is termed saccha- 
roidal when evenly g granular, like loaf sugar. It may also be 
eryptocrystalline, that is, having no distinct grains that can 
be detected by the unaided eye, as in flint. The term crypto- 
crystalline is from the Greek for concealed crystalline. Aphani- 
tac, from the Greek for invisible, has the same signification. The 
term ceroid is applied when this texture is connected with a 
waxy lustre, as In some common opal. 
Under this section occur also globular, botryoidal, and mam- 
millary forms, as a result of concretionary action in which no 
distinct columnar interior structure 1s produced. They are 
called pisolttic when in masses consisting of grains as large as 
peas (from the Latin pisuwm, a pea), and odlitec when the grains 
are not larger than the roe of a fish, from the Greek for egg. 
5. Horms depending on mode of deposition.—Besides the 
above, there are the following varieties which have come from 
mode of deposition : 
a. Stalactitic, having the form of a cylinder, or cone, hang- 
ing from the roofs of cavities or caves. The term stalactite is 
usually restricted to the cylinders of carbonate of calei 1m hanging 
‘rom the roofs of caverns; but other minerals are said to have 
a stalactitic form when resembling these in their general shape 
and origin. Chalcedony and brown iron ore are often stalacti- 
tic. Interiorly the structure may be either granular, radiately 
fibrous, or concentric. 
