Most 78 RPM records were made of shellac compounds (typally 1/3 shellac and 2/3 mineral compounds). It wasn't until the 1930's that records began to be made from vinyl.
FYI - there were originally 5 different recording speeds for records. . .8 1/3 RPM, 16 2/3 RPM (the speed for talking books), 33 1/3 RPM (the speed for most all LP albums), 45 RPM (the speed for single play records typically utilized by AM radio stations) and 78 RPM