[Gem] Amber (mostly done, but needs to spawn on deserts, and removed from underground (minus underground deserts if present))

[Argmaster]

This is a proposal to add amber to the game.

Physical properties:

• hardness in Mohs scale: 2-2.5
• density (at 20° C): 1.1 g/cm3

In game properties:

• behavior similar to other gemstones - provide special effect instead of stats

Modifiers

• light Tool Material Modifier Ideas #172

Spawn rules

• On beaches as an ore on the sand.

Related to: #1269

[careeoki]

You should also be able to find amber in sandstone caves, or below deserts (hopefully, with #556). Amber on beaches should be pretty rare.