Sick card from the current number 1 team in the MLB

I have expanded my collection of this card and now have 7. I got more on the way but I am very confused about something. Can anyone please explain the difference between the Lava and normal refractor variants? Please help

Do they go for anything?

Why is it so expensive

One more on the way but Max Kranick has really been amazing so far with 9 innings pitched and zero earned runs.