Coal

Allows you to dig deeper. usually you need 4, but the tier 3 tech will allow you to dig with only 3 coal.

Iron

Used in everything. Prioritize this to begin with. Get lots of it.

Swarmlit

Rarer than iron. Used also in mostly everything. To start you don't need much but as you start upgrading turrets and building more buildings, it will become more and more in demand.

Yellow

A common yellow resource used in upgrading the meta progression

Green

A rarer green resource used in upgrading the meta progression

Purple

Toughest to acquire purple resource. This will be the one in highest demand and always be the thing that's stopping you

Tech

Allows building of additional structures. On floors 1 and 2 there are lots of them, but they get tougher to find the deeper you go.

Alien

If you mine this, a monster will appear which will also drop two swarmlite. Just don't mine it and it's never an issue. But if you have guards nearby and are in dire need of swarmlite, go ahead and mine it. Take note however, this monster from this block is much more difficult than the monsters which spawn from eggs. Highly suggest having multiple soldiers on stand-by ready to deal with it. It will be a "red" looking monster, indicating maybe it's an "elite" version of the normal monsters.

Monster Eggs

Spawns little monsters randomly, up to 5 or so blocks away. A bit tougher to mine out as they take a few more hits then normal dirt. Later difficulties they can take a large pounding before being destroyed. If there are currently no active monsters spawning, you should prioritize this all the time

Spawning monster

Created from monster eggs. This shows a location where a monster is about to appear.
You should instantly go for this all the time as soon as you see one, even if it means you need to stop mining whatever it is you're mining.

Shield

This make all blocks in a 3x3 grid adjacent to it very tough to mine. You should either directly go for this if it's in your way, or flat out ignore it. If there is only a single tile to mine within its protection radius, just go for that single thing instead then move on. If there are multiple, then definitely mine it out to prevent the protection. Also the oscillator makes it super easy to mine these. As does using the resonant laser to instantly zap it.

Lava Jet

Periodically shoots flames 3 tiles out in all directions where there's a red circle on it. Comes in various forms... can have 1 flame jet or up to a maximum of 4. You won't see the three and four variants until you get into higher difficulties or go much deeper. At difficulty 10 you might start seeing 4-way jets as early as 50m deep. If you're unable to safely mine it, it's best to stay away from the jet, wait for it to fire, then immediately focus mine it with your workers. Typically you can bust them before they fire again.

Boulder

If you are under this and mine out the tile below it, you will instantly die. You can crush many workers this way. Sad day. Never mine from the bottom. Mine it out from the sides or the top. If you don't have extra vision, be VERY careful about mining upwards as you never know if there's a boulder above the tile you're mining... Better yet, just don't mine upwards until you get the technology tier 1 vision upgrade.

Webbing

Mine these out as you come across them. If you leave them behind they slowly start to duplicate themselves and can start taking over the zone. Easy to mine and never an issue as long as you stay on top of them.

Sand

Basically like a boulder, but delayed. As soon as you mine out what's beneath it, it will shake a little bit and after a few seconds, will drop. If you have workers below, they'll get killed.

Snowfall

Mostly a nuisance block. If you mine out anything under it, it will drop snow directly below it. The snow will slow the effectiveness of your workers. After a few seconds a new snow block will appear on top of the next available surface, building up a snow wall of sorts. Just mine them out as you come across them to avoid them being a bigger problem later.

Frozen Explosion

Always ignore these things. If you mine one, all workers surrounding it, as well as all other blocks, are instantly frozen. Freeze lasts several seconds. However for each tile you fall after freezing, you take substantial damage. If there are a couple tiles of empty space below you and you freeze, you're at extreme risk of dying. Furthermore, the frozen blocks it leaves behind are a major pain to mine out as they're very durable. Ultimately, do everything you can to avoid mining these out... let them rest in peace. If you absolutely must mine one, make sure there's no space below your miner and come at it from the side while having solid ground right below you. Or, zap it with the resonant laser day time ability.

Freezing Jet

Like the lava counterpart. Except this one freezes your workers. It's only tragic if you get frozen and you have empty space below you, causing you to take fall damage. Try to take them out from an angle they aren't spewing, or at least make sure there is ground below you if you must take it head on.

Snowstorm

Creates a 2-tile radius snowstorm around it. This just slows your workers down and halves their mining speed. Not that big of a deal really but it can become a quick problem if a worm is about to spawn, or there are monsters that are starting to thaw within its radius. Take these out when it's safe.

Frozen monster

Once you get within 2 tiles of these frozen monsters, they being to "thaw". It takes awhile, but eventually they'll be a little chomper dude that runs around wrecking havoc. At night, they will re-freeze too if you've not dug them out. If they are along your mining path, make it a priority to mine them before they unfreeze.

Ice Shard

Treat this like a boulder. As soon as you mine it, a large frozen spike drops directly below it, inflicting massive damage to whatever it hits. Usually it will break a block below it, but some tougher blocks it might only just severely damage it. Your workers will get insta killed.