Thursday, June 13, 2013

the Brunton

I'm not sure how much this diminishes my credibility as a geologist, but I do not own a Brunton compass.

(photo from here)

What distinguishes a Brunton (sorry, pocket transit) is that you can measure dip angles and compass headings with remarkable precision, it's small (if not light), and it's bulletproof. The ones we used in college and grad school had been manhandled by generations of students and worked fine.

Last time I needed to determine fracture orientation in the field, I had to scrounge around for a pocket transit that I could borrow from someone else, since my organization didn't have one. When I started asking around, I found that about 20% of geologists had their own pocket transit. My sample may be biased low, because these were the people who knew I was looking to borrow one. Other owners may have kept quiet because they weren't willing to share an admittedly expensive gizmo.

The pocket transit I used worked out fine, but since I was using a personal, very expensive item, I was petrified of dropping it or scratching the mirror - a real possibility, considering the rocks I was scrambling about on. I've been keeping an eye on eBay - they turn up regularly at prices ranging from less than $100 for dusty old finds to $700 or so for unused ones.

If I were a structural geologist, I'd definitely have a pocket transit. But I rarely need to go out and assess outcrops. Readers, if you do structural-type stuff a lot, do you still use a trusty 50+ year old product, or do you have something newer/fancier/better?


c said...

Great post! I own, and use extensively, two 1960's Bruntons, mostly for exploration geology mapping in Northern Canada. These are really versatile instruments.

Anonymous said...

Never trust a geologist who doesn't have a brunton.
No, I'm totally kidding, those fuckers are expensive.
My old structural/sedstrat prof epoxied little level bubbles onto regular compasses, and attatched a mirror and some other shit. Basically it was macgyver'd magic. I loved it.

Silver Fox said...

I still use a Brunton, my second version so far (don't remember what happened to the first one, which I was required to buy for field camp), and will someday (soon?) upgrade to an azimuth version, because mine is still old fashioned enough to use N xx W and N xx E, etc.

I use it for any mapping I do, and have used it for claim staking.

Anonymous said...

Well, if lack of a Brunton diminishes one's credibility as a geologist, then mine's completely shot. The last time I had my hands on a Brunton was in the late 70s in university (about the same time I last used a plane table and alidade). My 30+ years career since then has all involved cuttings and core, for which a Brunton has limited utility. I've done a bit of hobby mapping and for that my old Silva Ranger is "good enough".


Rock Head said...

I'm old school about teaching intro geology students about the use of a Brunton.

However, I have a couple of apps on my Android phone that can be used as a substitute for a Brunton in a pinch: a compass app for strike (as long as you remember to reverse NE and NW) and a clinometer app for dip. The compass app also displays true north vs. magnetic north.

Daisy said...

I just bought two Bruntons with my first research grant. It was a very exciting purchase, I never go anywhere without it! I'm a structural geology type.

A Life Long Scholar said...

I own a Brunton, and have since my my undergrad days (thanks to my mom and step-dad!!!!), but having done work in Australia I must say that I would FAR rather have the sort of structural compass they use there, since they are MUCH easier to use. Instead of measuring strike and dip desperately one sets the bottom of the compass on the outcrop and both adjusts the hinge of the compass such that the hinge line is parallel with the strike and the compass body is parallel with the dip. One then reads the dip direction (instead of strike) off of the compass face and then picks up the compass and looks at the markings on the hinge to read off the dip.

This means that one can measure dip in places where it would be hard to get one's head to look at the clinometer of a Brunton, since the instrument remembers the dip until you move the hinge.

Sadly, I don't recall the name of this sort of compass, but the last time I looked them up they were way more expensive than a Brunton, and I couldn't afford it. Now that I might be able to afford one I am not doing any field work, so I haven't bought one, yet...

Joe Kopera said...

I use a Breithaupt Stratum transit-- it's a better designed and built version of the Brunton Geo. for roughly the same price. But I'm also a structural geologist who takes about 3-4000 measurements a year during production mapping, so it's worth it to have something well made that works for me.

Christie Rowe said...

I'm a structural geologist and I've tried lots of options but the Brunton is the only one that has the precision I want in strike and dip measurements. The calibrated hinge type is much faster to use though. It really depends on the level of precision that you need for the work you are doing. I think for a lifetime purchase, a Brunton is a fantastic deal.