Red sandstone

Red sandstone is the ingredient used to create robust glass after As a First Resort.... It requires 81 Mining to obtain; this requirement is boostable.

Completing the quest As a First Resort is not required to mine red sandstone. However, the quest As a First Resort is required in order to melt red sandstone to create robust glass using the robust glass machine.

There are 2 locations where red sandstone can be found: the Oo'glog red sandstone mine slightly north of Oo'glog, which produces 50 blocks a day, and the Sophanem red sandstone mine just outside the east gate of Sophanem, which requires completion of the elite Desert tasks and produces 25 red sandstone.

Mining this yields 70 experience per block, but players are only able to mine a maximum of 75 red sandstone per day, which resets at midnight UTC. Note that even though only 75 can be mined per day, there is no limit to the amount of robust glass that can be created per day. There is no level requirement to make robust glass.

Uncut gems and strange rocks can be received from mining red sandstone.

According to Rutmir Arnhold, the walls of Oo'glog are composed of red sandstone, but the ogresses won't let anyone mine them for obvious reasons.

Shooting Star
It is possible to mine more than the maximum daily amount with the reward from shooting stars, which gives the player a chance of receiving double ore. Assuming the player is mining all the red sandstone available, the effect of the reward given by the shooting stars will allow the player to mine up to about 34 extra pieces per day. However, the extra-ore effect of Varrock armour does not allow you to mine multiple pieces of red sandstone.

Resourceful aura
The Resourceful aura can also be used to slow the depletion of the rock so that more than 50 (75 if the Desert elite Tasks have been completed) can be obtained per day.

Collector's Insignia
The Collector's insignia can also be used to slow the depletion of the desert red sandstone rock, however it doesn't appear to work on the Oo'glog one, this is likely a bug.

Trivia

 * Red sandstone alludes to the parallels Oo'glog has with the Australian outback, a remote, rural area in which the topsoil is red.
 * On the day of release, red sandstone was tradeable, but this was changed by an update to prevent an excessive influx and a decrease in prices for flasks.
 * Unlike the animation for mining concentrated ore, which continues as if no ore was mined until the player's inventory is full or the deposit is emptied, the animation for red sandstone restarts after each successful attempt.
 * On 7 September 2012, the rock from which you mine was moved a few squares south.