XRD analyses allow the identification of minerals based on their atomic structure. During XRD analysis, X-ray beams reflect off parallel atomic layers within a mineral over a range of diffraction angles. Because the X-ray beam has a specific wavelength, there are only specific angles which the exiting rays will be detected and counted by the detectors. Every substance has a unique diffraction pattern that can be used for identification. With this instrument, scientists can evaluate the mineralogical composition of sediments and the alteration products of ocean crust material.
XRD analyses were done on powdered samples. Quantitative analysis of a powdered sample of unknown composition is a difficult problem. An analysis program on the data acquisition computer could be run to analyze the results. After 1991, a freeware program for the Apple Macintosh platform called MacDiff was available to the scientists for a quick qualitative and quantitative analysis of samples. For more thorough analyses, scientists could take XRD files to their home institution.
Samples were normally ground to a fine powder using a Spex mill or mortar and pestle when the sample was very small. The powder was pressed into a sample holder or smeared on a glass plate that was placed into the sample holder. Prior to Leg 147, XRD analyses were collected on a DEC PDP-11 and the files archived on floppy disks. Data analysis software could be used to create a printout of the diffraction peaks. Occasionally, a spectral plot or the quantitative analyses was also printed. Starting with Leg 147, the data acquisition software was moved to a personal computer–based system with the raw XRD files written to disk.
The analysis and interpretation of XRD diffraction data were the responsibility of the Shipboard Scientific Party. Sometimes, the scientists on a cruise were not familiar with the interpretation of XRD data. For several ODP legs, there is no mention of XRD, even though samples were analyzed.
Prior to Leg 147, XRD raw data files were copied onto DEC PDP-11 floppy disks. One copy remained on the ship, and one copy was archived at ODP/TAMU. The printouts of the diffraction peaks and any plots were brought back to shore and microfilmed for archival storage. After the transition to the personal computer–based data acquisition system, files were written to disk and transferred to shore and archived on ODP/TAMU servers.
The DEC PCP-11 system was deactivated, sent back to shore, and eventually accessed. Unfortunately, the data stored on those DEC floppies could not be retrieved, partly because the computer system was not capable of being put onto a network. The raw data for the XRD analyses before Leg 147 were no longer accessible.
The data model for XRD data can be found in "Janus XRD Data Model" in "Appendix Q." Included are the relational diagram and the list of the tables that contain data pertinent to XRD analyses, the column names, and the definition of each column attribute. ODP Information Services Database Group was responsible for the migration of pre-Leg 171 data to Janus.
Archival of XRD data in Janus consisted of extracting the header information into a table. The header information from the XRD data file documented the system setup and data acquisition parameters. The entire raw data file was then copied line by line into a table designed to hold the text of the data files. Migration of data for Legs 147–170 was done in the same manner.
Pre-Leg 147 data could not be uploaded because of the lack of data files. Advances in scanning technology gave ODP/TAMU Information Services the opportunity to scan the pre-Leg 147 printouts and upload those images to the database as Primedata images.
XRD raw data files can be retrieved from Janus Web using a predefined query. The XRD query Web page allows the user to extract data using the following variables to restrict the list of available data files: leg, site, hole, core, section, depth, or latitude and longitude ranges. Table T35 lists the data that are retrieved from the XRD query. To extract the data file, the user must click on the Data File link. Currently, there is no other way to download all files of interest from Janus Web. The user can contact the IODP/TAMU Data Librarian for help when requesting a large number of the XRD data files.
"Description of Data Items from XRD Query" in "Appendix Q" contains information about the format of the archived ASCII files. Data header format differed during some legs (see "XRD Data Header Format" in "Appendix Q").
The name of the file in the archived ASCII set is the full sample identification. The first line of each data file contains an abbreviated sample identification text string. For samples from Legs 147–180, that identification was manually entered by the operator or scientist. Usually, there is no leg identification and the site number may be shortened. Starting with Leg 181, the database-assigned Sample_ID was inserted in the first line in order to ensure the data were being linked with the correct sample and to speed the upload of files to Janus,. This change made it very difficult to determine any information about the sample by looking at the first line of the file.
Almost 16,000 XRD analyses were done on samples during ODP. It is unknown how many have been analyzed for their mineral content.
The modification of the sample identifier in the first line of the XRD file significantly improved the accuracy and integrity of the XRD data in Janus, but after the file has been retrieved from the database, the user must be careful to document the file in such a way that its location is not lost. The Sample Report query on Janus Web does retrieve Sample_ID, but there is currently not a way to enter a Sample_ID and have the query return its location information.