Asian Jade Stamp

Can anyone provide information on this Asian Jade Stamp I have? Any input would be greatly appreciated!

 

The script is awfully stylised, but perhaps 米市山可 - Michi Yamako (a name). What makes you think it is jade? From the lustre it looks more like a black hardstone, jade would usually have a smoother and shinier finish. It doesn't look particularly old but it is difficult to assess from images.

 

Not really sure if it's jade. I purchased from an antique shop and description was jade. Perhaps it is black hardstone. Can't find any info on it. Thanks for your reply. I was looking to sell it, but have no idea of the value.