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LETTER XXXV. 
OPALINE WOOD THE RESULT OF THE UNION OF SILICIOUS AND 
SOFT BITUMINOUS MATTER. 
Wk shall now proceed to the examination of that kind of silicious 
wood, in which the influence, and, indeed, the presence, of bitumen, 
appears to be still more apparent. 
Opaline wood, Iloh Opal of the Germans, Quartz-resmite xyloide 
of Hauy, or silicized bituminous wood, is characterized by a peculiar 
waxy, or rather, resinous lustre. Its fracture is conchoidal, and it 
generally shines with the particular lustre just described. Sometimes, 
the fibrous structure of the wood which remains will so direct the 
fracture, that the fragments will be linear, or laminated. Its specific 
gravity is from 2.045 to 2.675 ; and its hardness is such, that it will 
frequently yield sparks freely, on collision with steel. 
In this, as well as the other kinds of petrified wood, we are 
astonished at discovering the nice state of preservation, in which the 
fibrous structure of the wood exists, whilst it has undergone so vast 
a change in the nature of its substance. This, it has been already 
remarked, appears to have been accomplished by the bituminization 
of the wood itself; and in this kind the bituminization appears to 
have been more perfect than in the preceding kind. By this process, 
although the disposition of the fibres is frequently not at all altered, 
its nature is changed ; and it is rendered susceptible of an impreg- 
nation, with a fluid holding earth in solution. 
The specimen depicted at PI. II. Fig. 7? appears strongly to cor- 
roborate this opinion respecting the conversion of the ligneous into a 
bituminous substance, and its subsequent impregnation with silicious 
particles. In that specimen is a knot of the wood, which differs 
VOL. I. 
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