25 January 2012

Rocks in the kitchen (Accretionary Wedge #42 Entry)

Posted by Jessica Ball

Ian Saginor of Volcanoclast is hosting the next Accretionary Wedge, and it should be a neat one: we’re supposed to explore the geology of the indoors – specifically, countertops. Here’s the challenge:

Have you seen a great countertop out there?  Sure, everyone says it’s “granite”, but you know better.  Take a picture, post it on your own blog or send it to me and I’ll post it for you.  Do you think you know what it is or how it was formed?  Feel free to include your own interpretation and I’m sure others will enjoy joining in the discussion.  Ron Schott suggested that we expand the entries by including any decorative stone material that has been separated by humans from it’s source.  This includes buildings, statues, etc.  There’s a lot of really unusual stuff out there, so make sure to find a good one.

I was excited about this, because I have the perfect entry. It’s also the reason that I really don’t want my parents to move out of their current house anytime soon, because then I wouldn’t be able to stare at the kitchen counters. (Thanks to my mother for taking these photos, by the way!)

When my parents ordered this they sent me a chunk, and after it made its way around the department at UB, we all agreed that my parents ended up with skarn rather than granite. But that’s okay, because it’s not your run-of-the-mill granite countertop – it’s much more interesting! In fact, it’s kind of like walking into an exhibit on metamorphic mineral assemblages! My dad was a little concerned at first about the durability (I warned my parents off of succumbing to the lure of marble in the kitchen), but he was reassured to find out that calc-silicate minerals are pretty durable. I was actually really impressed that they picked out something so interesting – my geologic obsession is rubbing off!

Skarn, in case you’re not familiar with the term, is a calcium-silicate-mineral-rich metamorphic rock usually formed from the contact metamorphism of an igneous intrusion (like granite) with some sort of carbonate. In the case of my parents’ counters, the mineral assemblage includes lots of wollastonite (the white crystals), garnets galore, quartz (some of the gray crystals), and probably some pyroxene (the darker minerals). I spend most of my time staring at the garnets, some of which get pretty big, and which are scattered over all of the slabs.

There are also some pretty big wollastonite crystals here and there (the ones below look like they might almost be a vein of wollastonite, although there’s something else filling in the cracks – maybe calcite). As you can guess, when I visit I spend about as much time in here with my nose pressed against the counter as I do actually cooking.

The funny side of the story is that my parents knew what they were ordering might not really be granite (since I’d warned them that “dimension stone” purveyors tend to slap that label on everything) – and when they were asked to fill out a customer satisfaction survey, responded along the lines of “the counters look great, but our daughter the geologist said you might want to check your labeling a little better, because this is nowhere close to being granite.” I suppose if you wanted to stretch you might be able to say that it formed near a granite at some point…Unfortunately, we couldn’t dig up the actual quarrying location from the information the purveyors provided, but maybe it came from someplace like a Canadian shield mining district.

The dimension stone people never wrote back about the survey, by the way. Either they were too embarrassed at being told by their customers that what they were selling wasn’t granite, or they don’t really care about the surveys (probably the latter). Still, it’s a good thing to remember if you’re buying a stone countertop – don’t trust the salespeople, but keep an eye out, because you might find some pretty cool rocks to install in your house!