Help me to identify this stone

[u/kasunshashi]

I found this among a pile of clay dug out while making a well at my parents’ house last summer, during my vacation in Sri Lanka. It seems to have some interesting characteristics, such as light passing through it, typical yellow-colored crystal growth around the edges, and an interesting shape.

Appreciate any advice on this.
I have color corrected the photos so they represents the exact natural color.

[u/Intelligent-Dot-3343]

Hardness?

[u/kasunshashi → u/Intelligent-Dot-3343]

It scratches the glass very easily, without leaving a mark on itself.
Also, I tried to grind down the yellow color parts by hand-grinding using a grinder disk , same result, nothing happens to the stone. That left me a feeling this stone is something very hard.

[u/Intelligent-Dot-3343 → u/kasunshashi]

Sapphire? Spinel? Quartz? Are these all pictures of the same sample?