 In this module, we learned about igneous rocks. So these crystalline assemblages that are formed from lavas and magmas that have crystallized either beneath or at the surface of the earth. These are made up of silicate minerals that are very resistant to weathering, and they're also very, very hard. So the physical properties of these rocks is an amalgamation of the physical properties of the minerals that make them up. But in summary, they come together to form a very hard, very resilient, very lasting rock that will be around for geological time scales, which are on the order of millions, hundreds of millions of years. I've seen basalts that are over two billion years old. So we're talking about stuff that could stick around for a long, long time here, and this comes into play in some of the ways in which it's used in art history. Very much so. Yes, as I hope you have noticed, the common thread running through our case studies is that all of the works we looked at were meant to be permanent. And in the case of some of these sculptures, we actually have inscriptions on them from ancient Near Eastern rulers that said, I chose to have this made not of gold, not of bronze, not of lapis, which was very expensive, but instead of basalt or of diorite, so that it would last forever. And it's that lasting forever that is one of the most important commonalities that we have. And that comes with a difficult side, as I hope you also noticed, for the artist, because unlike some of the softer rocks that we're going to investigate next, it is very difficult to work with diorite and basalt, here's my diorite, and with porphyry, you have to work it punching into it perpendicularly, rather than being able to kind of slice it off or shave into it the way that you can work with tools in marble. And so there is an extra level of effort and of difficulty just in shaping and forming it. But then the payoff is that permanence.