Laterite?

[calura]

Almost a year ago, I bought some special stones for aquariums. My intent was to resell them, but things happened.

ANYWAY, I now have about 15 lbs each of rainbow stone (sandstone) and something called Exotica Fire Rock. The best guess I can come up with for fire rock is laterite. Laterite can have the same "fire" striations in it that this fire rock seems to have. It's definitely natural, because I broke it and the color continues through out the rock. Many aquarium rocks are "painted" limestone, so when you break it, the inside is just white. Not the case here.

Has anyone ever had this, and has anyone tumbled it? It appears to be everywhere on the Mohs scale from 1 to 5 - mostly depending on how long it has been exposed to air, as being exposed to air makes it harder. There are even sources that say it has to be collected as mud. But it seems to be kinda like brick except that it doesn't take super-high heat to turn into such a hard material - just air. 

I can say that I hit this thing with a dead blow hammer many times without breaking it. I finally had to get a screwdriver to help chisel some off to check and see if the color was painted on or true.

If it's a hardness of 1, there's no point in tumbling it because it will just turn into mud in the tumbler. But I'm pretty sure this is much higher than a 1 on the Mohs scale because that dead blow hammer wouldn't break it. I'm tempted to start it up anyway (I only have a rotary) at the absolute slowest speed, and check *every single day* for progress.

The good news is if it tumbles well, I can display it in my 120G in my foyer, because I have already had two large pieces in there since I first got it and it hasn't affected the water parameters.

Anyone else have experience with this stone and tumbling it?

[vegasjames]

Laterite is not a singular thing. It is a byproduct of weathering in tropical and subtropical areas creating various byproducts such as some bauxites. Laterites from soil to a hardened rock.

I collect my red selenite crystals in a laterite layer just outside of Las Vegas. In this case the crystals are more in a layer of an iron rich clay material with some silica sand mixed in. The laterite was formed from pyrite that oxidized and formed sulfuric acid and iron hydroxide by reaction with rain water. The acid helped in the dissolving of stone to form the soil, and both the acid and iron hydroxide are solvents for metals. As these percolate through the soil, they eventually hit the ancient ocean bed here consisting of limestone. This neutralized the sulfuric acid forming calcium sulfate forming the selenite crystals, and the iron hydroxide formed iron oxide giving the red color to the lateritic soil and the crystals. Definitely cannot tumble this laterite as it is mainly clay. It is as hard as cement when dry, but as soon as it gets wet the clay turns rapidly to mush.

You can see the laterite layer at the bottom in tho picture with all the selentite crystals sticking out.



The selenite crystals

[parfive]

In the evening the port became beautiful for perhaps five minutes. The laterite roads that were so ugly and clay-heavy by day became a delicate flowerlike pink. It was the hour of content. Men who had left the port for ever would sometimes remember on a grey wet London evening the bloom and glow that faded almost as soon as it was seen: they would wonder why they had hated the coast and for a space of a drink they would long to return.

[lapidary1234]

I have never heard of this stuff but the way @vegasjanes describes it i can easily imagine it.

Its important to note that hardness is a materials ability to resist permanent indentation or scratching. This is different than tenacity which is a minerals resistance to breaking or bending (smashing). Take jade for example, jade has a hardness of 6-7 but is Very tenacious and hard to break if sashing with a hammer.