Re: Are diatoms used to make glass and are they in the silica gel packets?

Your students are very lucky to have a teacher that goes the extra yard to 
find interesting information to captivate their imagination.  All of your 
hypotheses are correct, but the deciding factor in most manufacturing is 
$$.
Glass is made from sand and soda ash.  The fusion of these 2 materials is 
called water glass or sodium silicate.  Sand is much less expensive than 
pure diatoms (diamtomaceous earth, which is abbreviated as DE).  The 
crystalline structure of SiO2 (sand or quartz) also make a better quality 
glass than diatoms (which are amorphous silica, not crystalline).  
However, because of the prevalence of diatoms on earth, I am sure that 
there are some diatom skeletons that can be found in the sand that is used 
to make glass, but they are not added specifically to the manufacturing 
process.

Slica gel is produced by reacting sodium silicate (water glass) and 
sulfuric acid.  Once again this is the cheap way to manufacture the 
product.  However, as I mentioned above there will be diatom skeletons in 
the mix due to their prevalence on earth.

Here are some other interesting uses for DE which are found in Hawley's 
Condensed Chemical Dictionary:

1. Filtration (swimming pools and aquarium filters use DE)
2. Clarification (Since DE is insoluble in water, it acts like a moving 
filter.  As it settles to the bottom it brings the other paticulate matter 
with it and clarifies the liquid.)
3. Absorbent (just like silica gel)
4. Mild abrasive  (mixed with water it is like liquid sand paper)
5. Anti-caking agent (added to fine powders to prevent clumps)
6. Drilling mud-thickener (who likes thin mud anyway!!)
7. Insulator (DE is a poor conductor of sound, heat, and electricity)
8. Extender in paints (once again we are stretching the bottom line $$)

Congratulations on a great question and for being a super teacher.

Mad Scientist Dave