It can be used to make a compound. I think it's not a suffix, since rijk is a word on its own as well.
- rijk = rich
- waterrijk = full of water
- voedselrijk = full of food
- schatrijk = filthy rich (literally it's treasure rich)
- belangrijk = important (lit. rich in importance/interest)
- kansrijk = promising (lit. rich in chance)
- vindingrijk = resrouceful/inventive (lit. rich in findings/inventions)
I love finding the places where English and Dutch's points of origin can be found. Words from each language that share a concept are so oddly close but not quite the same. For example, you said "kansrijk" is promising, or rich in chance, and based on patterns I've seen so far I'm reading the word "kans" to mean "chance" as in: It CAN happen, there's a chance. Am I making a stretch or is there a common origin in meaning there? :P Other examples are words like "achter" to mean "behind", which is obviously "after" but it's just not quite how we commonly use the word in English.
You should check out The History of English podcast. His examples of cognates from other Germanic languages are why I decided to start learning Dutch in the first place. It's so fascinating how similar English and Dutch are -- and it's interesting to see how and where they're different, as well. ^_^
Yes, and it's also similar to the German -reich. As adjectives, both rijk and reich can mean "rich"; as suffixes, they can both mean "full of", like -ful.
For instance, leerrijk = lehrreich (literally "full of teaching") = educational. If you're really lucky, you can even translate completely using cognates: mineraalrijk = mineralreich = mineral-rich.