Is natural gas considered a mineral?
No. Natural gas (aka Methane) is a gas.
Why is the ice in a glacier considered a mineral but the water in a river is not considered a mineral?
Ice in a glacier meets the requirements for being a mineral, because it is natural, homogeneous, solid and crystalline, and has a definite chemical fomula. River water is liquid and therefore also not crystalline, so it is not a mineral. If and when the river water freezes into ice (naturally), that ice is a mineral.
obviously the previous answer is incorrect, the true answer is that natural gas and oil is NOT minerals because they both lack a crystal structure and a solid form. +++ That's not correct either: I am not sure about natural gas, but oil is regarded as a mineral. Although many minerals are indeed crystalline, that property does not necessarily define a mineral. Coal, iron-ore and clay are amorphous minerals, too, for example.