Two-circle Contact Goniometer
The two-circle contact goniometer has a tripod brass base painted black. A small brass graduated disc is connected to the center of the base on a pedestal, and the center of this disc is allowed to rotate. A small pedestal is raised from the center of this disc for the placement of the mineral. A second large brass graduated circle runs perpendicular to the disc so that it arches over the disc and is connected to the tripod base on either end. A brass contact bar runs perpendicular to the large circle. One end of the contact bar sticks above the circle and has a knob, while the other end of the contact bar is near the center of the circle and bears a flat edge. A contact bar is bolted to a brass piece that surrounds the circle, leaving the graduated side visible.
To set up the two-circle contact goniometer, a crystal is placed on the specimen holder such that one crystal face is parallel to the graduated disk (also called the stage). The crystal face that is fixed to the specimen holder is selected based on the axis of a prominent zone. All measurements are taken in relation to this zone. Next, the contact bar is then positioned such that its end is parallel to and in contact with a second crystal face. The goniometer is used to find an intersection point between pairs of crystal faces. An intersection point can be visualized as a point which connects two perpendicular lines drawn from the two crystal faces. The intersection point is written as coordinates: one measured on the stage and one on the vertical circle. The stage has a range from 0 to 360 degrees. The vertical circle measures from 0 to 110 degrees. The coordinates can also be thought of as a polar distance and azimuth which are then plotted on a projection. Once all the intersection points have been determined and plotted, trigonometry is used to calculate the interfacial angles and indices.
Outer diameter of vertical circle: 15.25 cm
Inner diameter of vertical circle: 11.75 cm
Distance between the legs: 13 cm
Length of contact bar: 16 cm
Horizontal stage (circle): 8.5 cm
Overall height: 19.75 cm
Raised Center Disc
Both Graduated Circles
Unknown: Base of Stand
P.STOE | HEIDELBERG | GERMANY
Brass disc scale 1 to 36 by 10 degree increments
Brass circle scale 0 at the top center marked to 110 on both left and right side by 1 degree increments, marked every 5 alternating in larger and smaller line size.
Museum sticker catalog number DM3899
History of the Object
The goniometer was not widely used or produced until 1893 when a man who identified himself as Professor Goldschmidt began mass producing his goniometers. Goldschmidt designed several different types of goniometers, but began mass producing the contact goniometer in Heidelberg, Germany.This particular contact goniometer was manufactured in Heidelberg, Germany. The manufacturing date is unknown. The exact date and how Michigan Technological University acquired this particular goniometer is unknown. It was speculated that it was used to teach the mining students how to use the goniometer to identify various types of minerals. According to the staff at the A. E. Seaman Mineral Museum it is speculated that the Museum acquired the goniometer from the Geology department at Michigan Technological University.
1404 Sharon Ave, Houghton, MI 49931
Museum sticker catalog number DM3899
Gillispie, Charles C. Dictionary of Scientific Biography. Vol. 3. New York, NY: The American Council of Learned Societies, 1971. 61-62.
Spencer, Leanord J. "Goniometer." The Encyclopedia Britannica. 11th ed. Vol. 12. Cambridge, England: The Encyclopedia Britannica Company, 1910. 234-35.