Polishing Granite or Basalt

Quoted text begins.a glass-like surface but a cloudy finish without the deep, clear luster.
I have gone up to 3,000 to 5,000 to 10,000 grit
End of quote.

Basalt (and "black granite" aka gabbro) is more difficult to polish
than types of granite because it is not as dense, there being little
or no silicate material.

The fine abrasives you are using will polish over the top of scratches
and pits left behind after using earlier, coarser stones.

I suggest you go back to 120 grit, then spend more time and care at 220
and 400 grits. The later stones can then build on this good foundation,
producing a lustrous shine.

If you still have trouble, you can blame the stone. Less dense material
that has been sourced close to the surface of the quarry may be partially
weathered, or else may include softer minerals such as iron oxide.

Some "black granites" are stained with oils prior to shipping,
enhancing the dark colours, and hiding the poor polish.

Simon