AS 1141.26:2019 pdf download.Methods for sampling and testing aggregates Method 26: Secondary minerals content in igneous rocks.
5 Apparatus
5.1 General
Apparatus for facilities reporting on, but not preparing, thin sections are set out in Clauses 5.2 and 5.3. This clause lists both essential apparatus and optional apparatus; the latter being useful for more detailed examinations but may not be required for this method. The apparatus to be used by facilities preparing thin sections as part of this Method is given in Clause 5.4.
5.2 Essential apparatus
For examination of thin sections, the following apparatus are required: Petrological (polarizing) microscope, fitted with low-, medium- and high-power objectives and with eyepieces of various powers (typically 6X to 150X).Microscope accessories, including a mechanical stage unit, first order red and quarter-wave compensators and a quartz wedge. Automated point counter, with a grid of at least 300 points but preferably 600 points.
6 Preparation of thin sections
6.1 General
Rock thin sections used in this method may be produced either by a specialized commercial laboratory, operating automated or semi-automated equipment, or by the organization conducting the analysis of the thin sections. In either case, the finished thin sections shall be of a uniform thickness of 0.03 mm over most (see note) of its surface. The thickness of the thin sections is determined by examining the interference colours (birefringence colours) of known minerals under a microscope as the thin section approaches and achieves the specified thickness. Apparatus for the preparation of thin sections is set out in Clause 5.4.
NOTE Some excess thinning of the edge of the rock slice may occur during grinding. Provided the area affected represents a small percentage of the prepared slide (less than 5 %), the slide may be acceptable for use in the opinion of the person conducting the analysis.
6.2 Sampling
The test sample shall be prepared as follows:
(a) Obtain a sample of spalls, drill cores, boulders, or aggregate in accordance with AS 1141.3.1 orAS 1141.3.2.
(b) Select sufficient sample to prepare three representative thin sections of each identifiable material type in the sample.
6.3 Commercial preparation of thin sections It is common practice in Australia to have petrological slides prepared in specialized commercial laboratories that operate automated equipment capable of producing slides that are of uniform thickness throughout their surface area and conform to the requirements given above. NOTE If this service is used and if the laboratory is contracted for additional services, the laboratory should be informed of other analytical procedures that will be performed (e.g. Reflected light petrology and EDX) on the same sample in order that other thin sections or other specimens are prepared correctly.
6.4 Laboratory preparation of thin sections
From the sample selected, cut a thin sliver of rock from each sample with a diamond saw and grind one surface optically flat. NOTE In the case of aggregate, it may be necessary to produce composite sections by mounting a number of aggregate pieces on the same slide to ensure that sufficient section area is available to comply with the requirements specified in Clause 7(c). Mount the ground surface of the rock sliver to a glass microscope slide using epoxy resin. Grind the rock slice using grinding wheels and abrasive grits. Keep the thin section uniform in thickness during grinding over most of its surface and continue the grinding until the thin section becomes translucent. Continue grinding with fine grits, checking the thickness of the thin section at regular intervals by microscopic observation of the interference colours given by some known mineral in the section when covered with a film of water. Reference interference colours are shown in standard reference books. The thin section will be at the required thickness when the observed interference colours match those in the reference. Where it would assist identification, finished slides may be stained to assist in mineral identification. If required, mount a cover slip on the thin section.
7 Procedure
Determination of the secondary mineral content of rock specimens requires the analyst to hold a bachelor’s degree in geology or earth science or an international equivalent with majors in petrology and minerology. The analyst shall have at least three years’ post-graduate professional experience in conducting and reporting on rock petrology. This experience shall include training and experience in the assessment of mineralogy on the performance of aggregates and aggregate mineralogy, used in civil engineering applications.AS 1141.26 pdf download.
AS 1141.26:2019 pdf download – Secondary minerals content in igneous rocks
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