How much vinyl (content by percentage) is in VCT or Vinyl Composition
Tile (a popular "resilient" flooring material that is often used in
hallways and supermarkets)?

So far, I have found the following information that might prove
helpful in your search for the real composition:

My research thus far has revealed that all VCT seems to contain a minimum
of 85% limestone.  I want to know exactly how much vinyl is in the
remaining 15% composition that is found in VCT.  Many sites confirm
that VCT is 85% limestone - with the remaining materials being
binders, fillers, and pigments.  I am guessing there is somewhere
between 1% and 10% vinyl, which I'm thinking is used strictly as a
binder to hold the limestone together (after doing this research, I'm
thinking that VCT should have been named LCT or Limestone Composition
Tile!).

VCT is a HUGE commodity manufactured by several large companies
including Armstrong and Mannington (see list at
http://www.rfci.com/links.htm ).  It is ironic that VCT is classified
as a "resilient" floor, since 85% of it is limestone, a main
ingredient in concrete, it is basically as hard as a rock and not
resilient at all.

VCT is everywhere!  Because it is so inexpensive ($1.50 sq. ft.
installed) it is typically the floor of choice for supermarkets,
department stores, school hallways, cafeterias, etc...  you probably
even have VCT in your workplace somewhere (check the lunch room!).

Thanks for your help & goodluck!!  Please let me know if you need any clarification.