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Rock Library

The Oakdale Iowa Geological Survey (OIGS) facility houses an unusual collection called the “Rock Library”.  The Rock Library is a collection of rock samples that constitutes the primary resource for understanding Iowa geology. The library includes well chip samples from over 39,000 sites around the state, well core (cylinders of rock drilled for research programs) samples from over 1,700 sites, and rock samples collected at quarries and natural exposures by Iowa Geological Survey (IGS) geologists.

 Well Chip Samples

Well chip samples are small rock chips of that are washed out of a hole during well drilling. These samples are provided by well drillers, who collect the chips through successive five-foot intervals. The drillers also prepare a log in which they note the rock intervals penetrated, casing used, depth of water, and other pertinent information. IGS personnel visit well drillers to collect the samples and drillers’ logs. When these samples arrive at the OIGS, the information from the drillers’ log is entered into a sample tracking system and the well is assigned a unique number called a “W-number.” Next, the well samples are prepared for microscopic study and shelved for permanent storage at OIGS.

 To date, the Rock Library has well chip samples from over 39,000 wells, which represents over 10 million feet (1,900 miles) of drilling. The well chip sample program is largely voluntary.  Drillers are required to submit samples to the IGS for public access wells, for wells that produce in excess of 25,000 gallons of water per day, and for oil, gas, and mineral exploration wells.

IGS geologists study selected sets of well chip samples and produce “striplogs.” Each well chip sample interval is examined under a microscope to identify the rock types, proportions of each type, fossils, mineral grains, and other characteristics of the sample. This information is recorded on a form called a striplog. When all samples from a well have been studied, the names of the various geologic units encountered during the drilling are identified and indicated on the striplog.

 Well Core Samples

The Rock Library also contains cores from over 1,700 research wells, totaling over 400,000 feet. These cores are drilled using a special drill bit, which is impregnated with diamonds, that preserves a cylinder of rock in the center of the hollow pipe. Many of the cores in the Rock Library were drilled and donated by mineral research companies, mine and quarry operators, and environmental consultants. These cores are especially valuable for geologists, since the cores provide a nearly continuous look at rocks which normally lie deeply buried. The cores provide researchers with material to test the rock for minerals, identify fossils that are used in stratigraphic identification, test the rock’s porosity and permeability, and its structural properties.

 Accessing the Rock Library Electronically

GeoSam, an IGS web application, provides the public access to the information in the Rock Library.  GeoSam tracks the location of all the samples and cores stored in the Rock Library. GeoSam stores information on well locations, construction, and water production that drillers provide on logs. All IGS striplogs are and accessible through GeoSam. Other relevant information, such as a well’s stratigraphy, is also stored in and accessible using GeoSam.

 A Resource for Today and Tomorrow

The Rock Library represents an irreplaceable resource for the citizens of Iowa, with an estimated replacement value of $250 million. This wealth of geologic information will continue to grow as new samples become available, and IGS geologists will continue to prepare, preserve, and study these materials to make the information and interpretations available to all.

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Last modified on July 19th, 2016
Posted on July 3rd, 2014