Please see external links for images of buttons (front & back) made from the material(s) in question. ("NBS name" refers to labelling used by the National Button Society, USA.)
Natural materials
Animal-derived bone horn (To view reverse of button, hover mouse over image.) horsehair ivory leather pearl shell (Images of buttons made from all the shell types listed below) seashells:
land shells: emerald green snail shell
plant-derived
Rocks and minerals (or predominantly mineral-derived substances)
bauxite catlinite cinnabar coal enamel glass gypsum (a.k.a. plaster of Paris) marcasite metals: aluminium brass pot metal sterling silver steel whiteware ceramics: earthenware china
Synthetic materials
plastics
synthetic fibres synthetic textiles
See also Button collecting History of technology Seashells in personal adornment
References
Bibliography