Mohair is fiber from an Angora goat. Mohair is durable, sheds dirt, dyes well and does not felt easily. Despite its hardiness, it is usually spun into yarn used for fluffy garments and scarves. This yarn is abraded, roughing its fibers to create that 'fuzzy' look.
Angora is fiber from rabbits. Fabric made from this yarn is inelastic (no stretch), very fluffy, soft and warm. Contrary to a belief popular in the 1950s, a Angora sweater does not increase the size of one's bust.
Silk is the fiber produced by silk moths. Silk knitting yarn is made from damaged silk cocoons and broken fibers. 'Raw' silk still has the original moth secretions in it. 'Tussah,' silk obtained from wild moths is brown. The food fed to domesticated moths determines their silk's natural color; this can white, green or yellow.
Silk retains heat, absorbs moisture, pills less than wool, is very strong and very stable when knit, neither shrinking or stretching.
Cashmere is fiber from the undercoat of a Cashmere goat. It is so expensive because only a few ounces are obtained from each goat per year. It is such a delicate yarn, more fragile than wool and more susceptible to abrasion, that it is usually blended with wool to make it more durable.
Camel is fiber from the two-humped or Bactrian camel. Camel hair cannot be bleached, so it is either used undyed or dyed a darker color. It is lightweight and fragile.
Vicuna comes from the vicuna, a South American relative of the camel. They are rounded up once a year and shorn like llamas or sheep; their hair is finer than any other animal fiber.
Alpaca is a smaller relative of the llama but its hair is more commercially valuable. Yarn from this fiber does not felt or pill easily. It comes in fifteen natural colors (as do the alpacas) and is denser than wool, so fabric knit from it may droop. The undercoat of a llama is very similar to alpaca hair.
Qiviut (kiv-ee-uht) is included here because it is a wonderful Scrabble word; the fiber itself is very hard to find. It comes from a musk ox and resembles pale gray cashmere but does not shrink.