This is a glass fused ultrasonic replacement disc for the doTERRA Brevi diffuser.
If your diffuser is no longer producing mist, the ultrasonic disc is usually worn and needs to be replaced.
These discs physically vibrate at a very high frequency to break the water apart into vapor. Over time, the disc physically wears out and needs to be replaced.
This is just a normal part of maintaining a diffuser to ensure peak performance.