Is pyrite known in your country? Maybe it’s some kind of matrix pyrite or granite. I got one similar piece from Sweden in the mountaintops near a glacier. Also got the white matrix and some kind of shiny mineral inside. Some are transculent and some are solid but shiny as well. Here’s a comparison of granite, pyrite in matrix, and the rock I’ve found in Sweden last summer. Still don’t know what it might be but it looks like some mixture of quartz pulled down from the melting glacier where I found it.
Hope this help you out a bit. There are so many different kinds of minerals that even I can’t keep track of what I find.