I don't think having 6000 books defines you as a collector, it's just what you need to have a choice

When I was a child I collected stones and I had the most unusual collection of glass sherds. I had some blue ones that were very rare at the time.

I still collect stones- and I love if I have a piece of metal ore from Upper Calf Creek or a volcano lava from Santorini or La Gomera All my windowsills are full of stones. Some agates of Oregon beaches, green sand stone from Soest in Germany- they all remind me of my travels