Edit: I wrote that quickly in late night, so today I added my Result and also fixed some information.
You can do this by making a mask, with which you can map an Emission Shader with a Principled BSDF Shader. Set up your UV system first, you need the image to be projected perfectly on one of the faces, I picked the front one.
Second, find an image texture of diamond ore- I used this one
Then, in the Shader editor, we need to mask out the Ore from the stone.
First, take the UV coordinates and put them through a mapping node. With it, set the Location. If you want it centered, then add -0.5 on X and Y axis. Then, use Vector Math, set to scale to control the Scale of the image. Then, plug in the image texture. After that, if you scale it, you will see that it will repeat. So, that's why you have to set the image from
Clip. Now, you will have those diamonds to scale up and down with the scale node.
Now, Math node, set to
Maximum, to cut out the diamonds from the background stone. After this, feed it through Map Range node cut out the background completely. So, now you have a good mask. Then, use Emission Shader for the diamonds part, and Principled BSDF for the stone. Mix then with a Mix Shader node, with factor of our mask.
Now, if you plan on using EEVEE, you can check on Bloom in the render settings for that bloom effect. But, in Cycles, you need to go into the compositing and to add a Glare node, set to
Fog Glow effect, in order to get that bloom.
And that's it!