how can you tell the value of amber?

Answer 1

That's a hard question to answer. Amber can run anywhere from $5-100 per carat, but most of what is on the market to day isn't real amber. Remember, real amber is millions of years old. What most modern jewelry is made from is either a combination of amber and another material (like plastic resin) or it's actually copal, which is just few hundred or thousand years old.

Here are a few at home tests you can do to determine if it's amber, or something else:
1. Apply a few drops of rubbing alcohol or nail polish remover. Amber will remain the same, everything else will become sticky.
2. Amber usually floats in salt water, anything else usually doesn't.

Here's a short beginner's guide to amber:
http://reviews.ebay.com/The-Truth-about-AMBER_W0QQugidZ10000000000718039

Answer 2

Unless you are a gemologist, it is virtually impossible. Take it to a reputable custom jeweler. Most will be happy to look at it for you, and offer you a "guess-timate" of what it might be worth. A more thorough examination and certification will cost you, though.