Agate— Physical Properties ani> Origin 
and obscurely colored, it is called a "clouded" agate. 
In the so-called "eye" or "ring" agates the bands run 
in concentric circles. Agates made up of fragments 
of former agates cemented together arc known 83 
"ruin" agates (Plate IV). Characteristic agates of 
this kind are found in Schlottwitz, Saxony. Agates 
appearing to be made up of tubes or pipes cemented 
together are known as "pipe" agates. An important 
variety of agate is that known as "moss" agate, in 
which, as the name indicates, the agate has the ap- 
pearance of containing inclusions of moss (Plate V). 
These inclusions are often arranged in such a manner 
as to give the appearance of a miniature landscape, 
in which case they are known as "landscape" agates 
(Plate VI). 
Agates are generally formed in cavities in volcanic 
rocks. In the escape of gases and vapors from such 
rocks on cooling, cavities similar to those seen when 
pasty substances are heated are often formed and re- 
main open when the rock has cooled. The cavities 
are usually spheroidal in form or, more specifically, 
are often shaped like an almond, whence the term 
amygdaloidal, from the Greek word Tor almond, is ap- 
plied to them. The size of these cavities is also often 
about that of the almond but they may be much larger. 
It is in cavities like these that agates are chiefly 
formed, occurring as a filling that takes the shape of 
the cavity. Being of very tough material, which re- 
sists both physical and chemical corrosion, the agate 
nodules (the lumps or masses formed by the tilling of 
the cavities) are usually left intact after the rock 
about them has decomposed and hence agates are 
often found in soil or in beds of streams. In the lat- 
ter case they may occur far removed from the place 
of their origin. The size of the agate nodules varies 
according to the size of the cavity in which they are 
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