Continued polymer growth will result in deposition of amorph- 
ous silica from solution. Eventually, upon initiation of struc- 
tural ordering and further loss of water, opaline silica, 
SiOzenH20, forms. Ultimately (millions of years, unless sub- 
jected to high temperature and/or high pressure), opaline silica 
transforms through a series of stages to low quartz. 
A thorough discussion of the chemistry of silica can be found 
in ler (1955). Frondel (1962) treats in detail the mineralogy of 
silica. Geochemical aspects of the subject have been reviewed 
by Siever (1963, 1972). 
Technique 
In preparing siliceous petrifactions of plant material, the 
following procedure is employed. First of all, the specimen to 
be mineralized is boiled in water until it is thoroughly water- 
logged and gas free. Next, it is alternately immersed in water 
and ethyl silicate contained in separate ordinary canning jars. 
During treatment, the jars are sealed with rubber gaskets and 
stored in an oven maintained at 70 Celsius. Time of exposure to 
each reagent Is not critical and can vary from a few days toa 
month or more. The sequential operation is continued for a 
period of from several months toa year or more’. Several times 
during the course of treatment, when in ethy1 silicate, the jar is 
removed from the oven, uncapped, and placed into an evacuat- 
ing chamber. There it is subjected to vacuum for approximately 
one half hour or more to facilitate diffusion of liquid phase into 
the specimen. While the wood is immersed in ethyl silicate, 
caution must be exercised to avoid gelation of the entire fluid in 
the jar. This is probably brought about by drainage of excess 
water from the specimen. Should polymerization exterior to 
the specimen be indicated by a notable viscosity increase or by 
the appearance of cloudiness in the reagent, the specimen its 
immediately transferred to a fesh volume of ethyl silicate or 
advanced to the water cycle. During the final cycle in water, a 
‘The optimum conditions for the procedure — time of exposure to each reagent and 
of the entire sequential operation, temperature and pH during each stage of treatment, 
etc., are not known. Until the ideal parameters of the process are established, it is 
suggested that the wood be immersed in each reagent at four-day intervals, at seventy 
degrees, and that the sequential operation be continued for a minimum of three months. 
The procedure is most effective with small specimens of wood (less than 3 cm*) and 
large volumes of ethyl silicate (more than 500 cm*). Afterwards, the specimen should 
be stored in water. 
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