I cleared up the “ophitic basalt” debate, at least to my satisfaction, this evening. I went to a beach listed in my book to have a good amount of ophitic basalt, and it looks quite different to me than what I would identify as diabase (I found some of that there too).

Most of the rocks at Flood Bay are basalt. I’m still confused about how to differentiate ophitic basalt from diabase, though. One of my books draws a distinction, but another doesn’t. I read into it online, but I’ll have to keep studying in the field!

When I was in early elementary school, I really liked rocks, but my interest in minerals wore out sometime not long thereafter. When I was little, I remember looking through the gravel with friends, the prizes being chalk rocks, quartz and the occasional geode you could break open, which were my favorite finds! We used to have this cool nature and science store in the mall (where are stores like that these days?) which was my favorite store as a kid, and I used to like to go pick out polished, identified rocks for my collection. Maybe it was an early influence from my mom, who once wanted to be a geologist before she got into teaching. (We still visit some cool geological sites and she collects rocks.)  Anyway, it’s been a joy to rediscover that interest living on the shore of Lake Superior, and I looked for rocks with my parents when they came to visit for Labor Day weekend. The many-colored rocks on the beaches can’t help but inspire curiosity!

I got a small magnifying lens (I can’t find my loupe but I need another one if it doesn’t turn up…) to take with me on the beach, and re-examined some of my finds tonight in light of what I’m learning. I don’t know what magnification you need to tell rhyolite from basalt; in the “simpler” book I have about rock collecting on the north shore, the authors seem to distinguish by color. However, in the more complex guide to the Lake Superior shores, they say that the grain of the rock is what distinguishes the two. I looked at what I have so far and it’s hard to say if what I think is rhyolite is significantly “coarser” than the basalt. The samples seem to match the photos, so I’m just going to guess I’m on the right track so far.

I’ve found quite a few agates and fragments by now, most of them predictably small. I might need more mag to get at the features on the tiny ones. I’d love to find (or confirm among my collection) a brecciated agate. Breccia is formed when a rock breaks and is cemented back together. In the case of agates, I think the substrate can be anything, but I think breccia agate most commonly found amidst quartz and silica.

As highlighted in the feature photo, it’s hard to come to Lake Superior and not notice the rocks. There are seemingly so many different kinds of beautiful colors along the shore. I learned about agates and began looking for them along the beach, but I wanted to know about everything I was encountering, so I bought an ID book and have been visiting a few spots mentioned therein. After work today, I headed to the beach that is mentioned to have the most “vesicular” rocks among the spots listed. There were indeed giant blocks of vesicular basalt that were probably put there as something of a break wall.

This did seem to be a popular “rock hounding” spot though, so the agates were probably gone for the day. I noticed a few people looking for rocks while I was there. I picked up a few interesting rocks that I haven’t looked into much yet for identification.

This weekend’s drive up the north shore took me to a place I could see the namesake of Palisade rhyolite. I had planned to maybe hit Flood Bay on the way back, but it was late in the day and storms were rolling in, so I went straight home.