Okay, there are a significant number of questions but let me start with this. This sample is one with a stone inside another substance. So there are two substances here. The yellow substance. How hard is it? Well, you can't tell from a picture, so I would encourage you to try to scratch some yellow off. If it scratches easily and flakes off it could be a soft metal, like gold. If it is hard and you cannot get the substance to scratch, it could be quartz, diamond, citrine, topaz. If it is softer material and not gold it could be sulphuric, it could be flourite. It could be pyrite. Pyrite would be magnetic, gold would not.
The outside(husk) might be rhyolite, a volcanic rock. It is porous enough to allow elements and compounds in solution to permeate the husk and fill in voids. The resulting crystals are formed inside the host rock. Due to erosion and earth movement and weathering the rock inside gets exposed.