There are many types of mixed gemstones are rocks. Some mixes could be so weird, but beautiful. An example is: Quartz Crystal found in a piece of graphite, and much more.

Here are some images of mixed gemstones.

This is a piece of Quartz, with many pieces of gold in it.

These are images of the same rock that I took. It is a mix of many things. It is a granite rock with small pieces of Quartz, Black Tourmaline, Marble and some sort of metal that I can't identify. Rocks like this are pretty cool, in my opinion.

Mixed gemstones can be easy to identify, but if you're having trouble, you can always ask an expert. Sometimes, you can just as someone on the internet, like me. You can never know what you can find just below your feet. Be aware of your surroundings, because you can find many cool gemstones and minerals out in the open. If you don't care about those types of things, you can sell them at a fair price. Most preferably on eBay.