4.1 Petrographic examinations are made for the following purposes:

4.1.1 Determine the physical and chemical characteristics (mineralogy, texture, and composition) of the stone specimen that may be observed by petrographic methods and that have a bearing on the performance of the material in its intended use.

4.1.2 Describe and classify the minerals of the specimen.

4.1.3 Classify the stone both commercially and geologically based on Terminology C119, recognizing the differences in nomenclature; and based on the following standards, as appropriate:

Specification C406

Specification C503

Specification C568

Specification C615

Specification C616

Specification C629

Specification C1526

Specification C1527

4.1.4 Determine the relative amounts of the minerals of the specimen and constituents that have a bearing on the performance of the material in its intended use.

4.1.5 Compare characteristics of the stone with specimens from one or more sources, for which test data or performance records are available.

4.2 The petrographer should be told in as much detail as necessary, the purposes and objectives of the examination, the kind of information needed, and the extent of examination desired.

4.2.1 Pertinent background information, including results of prior testing, such as physical and mechanical testing, should be made available. The petrographer's advice and judgment should be sought regarding the extent of the examination. Available physical and mechanical testing may include the following:

Test Methods C97

Test Method C99

Test Method C170

Test Method C880

Test Methods C120

Test Method C121

Test Method C241

Test Method C1353

Test Method C217

4.3 This guide may form the basis for establishing arrangements between a purchaser of consulting petrographic service and the petrographer. In such a case, the purchaser and the consultant should together determine the kind, extent, and objectives of the examination and analyses to be made, and should record their agreement in writing. The agreement may stipulate specific determinations to be made, observations to be reported, funds to be obligated, or a combination of these or other conditions.

4.4 Petrographic examinations provide identification of type and varieties of minerals and structures present in the specimen. However, as noted above, identification of all minerals and structures present in the specimen is not necessarily required.

4.5 The petrographic examination should establish whether the specimen contains chemically unstable minerals or volumetrically unstable materials.

4.6 Petrographic examination should identify weathered or otherwise altered constituents or minerals and describe the extent of that weathering or alteration. Where possible, describe potential aesthetic changes that may occur as a result of weathering.

Note 1: If the dimension stone will be exposed to freezing and thawing and may become wet or saturated in use, finely porous and highly weathered or otherwise altered minerals should be identified because these materials will be especially susceptible to damage by freezing and thawing.

4.7 Petrographic examination should identify constituents or minerals and the extent to which they may lead to staining and color change of the surface of the stone when the stone is exposed to the weather for exterior use.

4.8 Petrographic examination should identify and estimate proportions of constituents that may be susceptible to deterioration from attack by deicing agents where proposed for use at grade level in freezing environments where deicing salts are anticipated to be used.

4.9 Criteria are available for identifying minerals by their optical properties or by XRD. Criteria are available for identifying rocks by their mineral composition and texture. Examination in both reflected and transmitted light may be necessary to provide data for these identifications. X-ray microanalysis using energy-dispersive X-ray spectrometers with scanning electron microscopy (SEM/EDX) or wavelength-dispersive X-ray spectrometers in electron microprobes (EMPA/WDX) may provide useful information on the chemical composition of minerals and rocks.

4.10 The objectives for which this guide was prepared, will have been attained if those involved with the evaluation of the specimen have reasonable assurance that the petrographic examination results, wherever and whenever obtained, may confidently be compared.