What is the effect of having a "rock" in the game? For example, 1/3 with $10 "rock". I believe the winner of the previous hand would get the rock and have to post $10 - does it also give the rock the button throughout the hand (pre and post-flop)?

Bump? No one knows?

The person who owns the rock posts it the next hand as a straddle. Action starts to the left of the rock, and moves around the table clockwise, giving the player owning the rock pre-flop position. Post-flop returns to normal. The rock goes into the pot so the winner gets the rock. I'm not sure who gets the rock in case of a chop. It's probably the OOP player.

Sometimes if you do not want the rock you can sell it to another player.

In my room we just wrap a rubber band or tape around a stack of chips which amount to the size of the rock. Some rooms which spread games with a rock often might have a special marker for it.

In my room the posting of the rock is mandatory next hand. I believe in some rooms you are not required to post it immediately, and may keep it (I believe until the blinds come around)

Does the rock have any monetary value? It's basically a mandatory Mississippi straddle yeah? Say you win and want to leave the next hand, can you take it and cash it out?

I believe the answer is yes to all of those.

literally never heard of this before - but might try it out at the next home game for fun. thanks OP

When I've played with it, the rock is a mandatory straddle. Generally can be played on the BTN, and must be played UTG if it's in your stack. Value depends but it's usually 2x the big blind. Other than as a straddle, it only has value if you're cashing out or you go all in.

Personally I hate the rock. In my experience, it's generally used in underground rooms with high rake caps in an attempt to juice the pot and hit the caps. When I play a game I basically ignore the rock or treat it as valueless.

the rock is a straddle with no money put in so you must play tighter as the stakes are higher but the blinds are not. in reality it should ruin the game.

To understand a rock, you first have to understand a straddle. So get that down pat first.

Once you understand a straddle, the rock becomes easy. A rock is a coupon for one free straddle. Like all coupons, there are rules and restrictions, and local rules vary.

In my home games, it simply raises the stakes somewhat. There is mandatory straddle, which raises the stakes the most. The straddle must be played by the winner of the last pot, regardless of his positions.

Then there is the situation where you must simply use the rock by the time the button gets to you (or before if you want). Most people except the real loose players use the rock on the button. This doesn't raise the stakes much since it's only used once every 5 or 6 hands on average.

If the straddle is used in the blinds, then the blinds usually must be put out along with it. For example, in a 1/3 game, if you straddle in the small blind it's the $6 rock plus the $1, and the big blind must call the extra $4 to play. Believe it or not, bad players actually do this.

While theoretically the straddle should tighten up the game, in my games it does nothing except cut the stack sizes in half and increase action. Of course, in most of my games the blinds don't matter - the game would play basically the same way even if we played without blinds. So much for theory.