If it leaves a gray streak, it may contain sulfite. A green or brown streak indicates pyrite. Feldspar, gypsum, mica, and talc leave a white streak. You can also try breaking your rock and looking at the way it splits, or cleaves. Feldspar splits into blocks.
Mica splits into paper-thin sheets.
Many minerals, however, break into very irregular surfaces. You may need to use another test to find out about them. Dr. Mora says. The Practical Geologist. With plenty of photos and illustrations, this book is an excellent introduction to geology.