Hard as a Rock

Makes it harder to mine non-ore stone blocks without explosives, and impossible to mine them without a high enough tool level.

Most types of natural stone will be harder to mine depending on how many of the same type of stone they touch.

For example, if you have a wooden pickaxe, mining a block of smooth stone is…
…fast if it’s not touching any other smooth stone
…slow if it’s touching exactly 1 other smooth stone
…impossible if it’s touching 2 or more other smooth stone

This makes it easier to break parts of stone segments that are “thinner” or “at the ends” and much harder to break eg. a solid floor or wall of smooth stone, making explosives more valuable.

Ores and other “non-monolithic” stone (cobblestone) don’t account for nearby blocks in this way, as they are more “crumbly”.

Mining speeds are rebalanced for non-enchanted pickaxes across the board, using mathematical formulas based on tool levels and block harvest levels, and you can’t mine blocks with higher harvest levels than your pickaxe at all (unless you use explosives).  The top pickaxe tool level in the modpack gets a little bonus speed.

In versions 1.12.2 and later, you can change which blocks “connect” to each other, making them harder to mine (and which blocks DON’T connect to each other).

Yes, you can use it in your modpack if you want (MIT license).

A list of my curseforge mods can be found here