Puddingstone is a conglomerate consisting of sharply contrasting by color pebbles of a round shape encircled by sandy or cement surrounding. It is also known by the names of pudding stone, plumb-pudding stone. In New Zealand, it is known as Puddingstone rock. It has been called so for its visual resemblance to the plum pudding or Christmas pudding (or a raisin).
Puddingstones date way back to the Huronian Period of the Proterozoic Era. Puddingstones are believed to be one of the rarest rocks in the world, although, it can rather easily be found in some places on the planet. The rock appears in a great variety of sizes from just a few inches to several feet.
It consists of small pebbles connected by silicon forming a solid rock. The plumb-pudding appearance of the rock can be best seen if the rock is broken - the pebbles give a cross section which gives this resemblance. Formed millions of years ago, they were deposited to the river bottoms and after covered by clay.
Over the centuries, the stones get compressed and during the Ice Age bound together, therefore, obtaining the solidity strong enough to resist being crushed. When the last Ice Age finished and the ice melted, the rock formations were tossed by the water and shaped into rounded blocks.
The Types and Locations of Puddingstones
There are various types of puddingstones which differ by the origin, composition and geographical location. The most well-known are Hertfordshire, Schunemunk, Roxbury, and St. Joseph Island (Drummond Island).
Hertfordshire puddingstone consists of flint pebbles, sand and silica cement. It is characterized to be brown to deep red with black exteriors and polished surface. This type of puddingstone is most commonly found in Hertfordshire and Plumstead Common in England. It mainly appears on the land surface in the form of concentration-like mass.
Schunemunk puddingstone is a part of thick geologic formation previously known as Schunemunk Conglomerate. Its features include grayish-purple to grayish-red color with pebbles of white vein quartz, red and gray chert, red shale. This puddingstone can be widely found on Bearfort Mountain, Boonton, and Rockaway Township, NJ, and Schunemunk Mountain.
Roxbury puddingstone consists mainly of the feldspathic sand matrix and well-shaped pebbles of quartzite, granite, quartz monzonite. It is a massive clast-supportive conglomerate that is usually found in Boston and Massachusetts regions.
Drummond Island puddingstones (or pebble jasper conglomerate, or Michigan puddingstone) consists of pebbles of red jasper, white quartzite, semi-transparent quartz in a coarse-grained quartzite matrix. The primary location where this puddingstone can be found is on St. Joseph Island and the area of St. Mary’s river on the northwest of Northern Ontario. However, during the repeated glacial advances, the fragments of this puddingstone spread across Michigan and to the Drummond Island and today can even be found as far south as Kentucky and Ohio.
Puddingstone can be easily polished and shows a spectacular variety of colors, which is perfect for jewelry and home decor accents.
Photo by James G. Kelley