The Accretionary Wedge is a semi-regular collection of geoblog posts that follow a common theme. Ian Saginor is hosting AW #42 at his volcanoclast blog with the theme of Countertop Geology. For my first ever Wedge, Ian has tasked everyone to:
- Find great countertops or decorative/building stone, as long as it’s been “separated by humans from it’s source”;
- Post some pretty pictures;
- …And maybe hazard an interpretation or two.
Good thing Ian expanded this topic to include decorative and building stone, because it opened up the opportunity to show off two awesome pieces from around the Notre Dame campus. First up is the Kugel Fountain in one of our student centers, the Coleman-Morse building. The Marble, as some call it, “contains a 30-inch solid granite sphere which weighs 1,300 pounds and floats on 7 lbs. of water pressure” (via the ND website).
Take a closer look…
The Marble was first described to me as an orbicular granite, which seemed to fit the rounded appearance of alkali feldspars (pink). However, in comparing it to other orbicular granites (thanks, Google!), I noted these feldspars did not exhibit the same patterns as other orbicules, namely crystals radiating outward and/or as concentric patterns. In addition, many of the rounded feldspars appear to be single crystals instead of layers. Fortunately, Ole Nielsen was there with a Olelog post on Orbicular Granites from Kuru, Finland, which led to this post on Rapakivi granite in the Sandatlas. Jackpot! (and thanks, guys)! Turns out The Marble is a Rapakivi granite orb, NOT an orbicular granite orb. Misconceptions: Busted! The term rapakivi is Finnish for crumbly rock after the tendency of the granite to weather rapidly when exposed.
PART TWO of this post focuses on a different sort of marble – the lithology instead of the shape. Walk into the Hesburgh Library and you get smacked in the eyeballs with meters and meters of marble slabs lining the concourse, administrative areas, and support columns.
Confounded and intrigued by the expanse, I asked our library Help Center for additional information. They did a wonderful job in uncovering an October 1967 article from Stone Magazine by then-Associate Professor of Geology Erhard M. Winkler, who wrote:
“Medium to dark gray polished Lido limestone-marble from Morocco dominates the interior walls for both the [library] concourse and the reading rooms of the first floor and the second floor. Imported by the Carthage Marble Corporation… The fine-grained limestone-marble is cut by numerous white calcite veins, which indicate strong shattering and subsequent repair with calcite from circulating solutions in the geologic past. A few dark gray clumps of irregular shape appear to be insoluble residues dating from a time when some solution took place within the rock, also in the geologic past. The diamond match of this distinct pattern gives the appearance of fine boxwork.”
The country of Morocco is on the NW coast of Africa and is part of the south side of the Strait of Gibraltar. Unfortunately, the Lido limestone/marble is such a popular decorative stone that I did not feel like spending the time to sift through the multitude of manufacturing and foreign websites to unearth anything useful. So instead, let’s all make our own interpretations!
There are obvious large-scale differences (competence? pressure? mineralogy?) in affected regions of the marble.
Calcite veins are neat and all, but what else is there? How about those “insolubles” that Dr. Winkler mentioned?
Thinking about this for too long marbles my brain, so I’ll leave it to y’all to quietly ponder amongst yourselves.