And what are yarns made of ...?

Technically speaking, you should never refer to acrylic yarn as wool. However, you can refer to wool as yarn. Further, the correct term for Alpaca and Llama yarns if fibre.

How can you tell the contents of your wool/yarn/fibre? Once again I refer you to your yarn band.
Contents: Llama/wool 70/30

I caution you against acquiring yarn that has no known contents. If you do acquire this yarn you must solve many mysteries upper most - care. Wools and other natural fibres require different care than does synthetic yarns.

There are ways to determine the contents of a yarn. This topic will be left for future posts.

Here is a brief list of wools/yarns/fibres which you may have the pleasure to cast on:

Ragg wool
Mohair
Lopi wool, Alpaca, Angora, Camel, Cashmere, Llama
Hemp/wool blend, hemp, banana silk, bamboo
Silk /Linen blend, silk, soy silk, linen, cotton, organic cotton, plant fibres
Acrylic, novelty yarn, polyamide (nylon), polyester, rayon.
Self-striping opal yarn

Here are some informative sites:

http://nutmeg.gen.nz/fakesheep/yarns.html

http://www.claacanada.com/a_few_fibre_facts.html

http://www.numei.com/fiberfacts.htm

http://www.binhaitimes.com/camel.html

Tomorrow's post: Twisted