Stone analysis techniques
- Petrographic examination, including:
- Mineralogical composition
- Stone type identification (commercial and geological typing)
- Deleterious feature identification
- AS 1141.26 – Secondary mineral content
- Failure investigation
- Material comparison
- X-Ray diffraction (XRD)
- Bulk estimated mineralogy
- Asbestos mineral screening
- Crystalline silica content estimate
Identifying features of concern
We can carry out these tests to determine the mineral composition, textural features, geological name, and commercial stone classification for marketing, identification, classification or standard comparison purposes. The tests can also identify potential features of concern before the stone is installed in a large project. Likewise, they are important for projects where the crystalline silica quantity is controlled for all materials to be used. Our team can even use these analyses as a tool to assist in determining the cause of a stone failure, such as cracking or warping.
Petrography and higher risk features in stone
Petrography is the microscopic analysis of a thin section of the stone (~30µm thick) through use of a petrographic microscope. Petrographic analysis is used to assist in identifying potentially sensitive features inherent to the stone type. Typically, a petrographic examination is used to supplement other physical property testing of dimension stone. This analysis ultimately informs the client about higher risk features and how these may affect the stone in service.
Asbestos minerals in stone:
The above test methods are highly important for projects involving stone types that are at a higher risk of containing recognised forms of asbestos minerals. These tests can be targeted to screen for and detect the presence of and identify the proportion of these deleterious/hazardous components within a stone sample. Asbestiform mineral fibres pose a significant health hazard when in a respirable form and inhaled or ingested. There are six main recognised mineral forms of asbestos: tremolite, actinolite, chrysotile, crocidolite, amosite and anthophyllite. However, it is important to know that there may be more naturally occurring minerals that can form asbestiform fibres. Read more about naturally occurring asbestos minerals HERE – Asbestos in dimension stone: The dangers and how to minimise risk
Images
1. Photomicrograph of tremolite asbestos crystal ‘aggregates’ in fibrous / elongate form when viewed using polarised light microscopy (Magnification 100x). Cross-polarising filter inserted.
2. Photomicrograph of a cluster of asbestiform chrysotile fibres intermixed with other various minerals as viewed under a polarising light microscope as part of the petrographic examination.
3. A piece of polished ‘green marble’ serpentinite. Often, green marbles contain a high quantity of serpentine group minerals such as chrysotile.
4. A piece of polished veined white marble. The circled area is a patch of a fibrous-looking material that was found to be mostly comprised of tremolite.
5. In white-coloured marbles, it is common for NOA tremolite to be identified in features such as opaque white veins or grey-white veins (circled) that look different to the surrounding stone.
“Understanding what a stone is comprised of is the first step to understanding how that stone will behave in different applications and environments. A stone with high quantities of mica minerals will be far weaker than a stone comprised of predominantly quartz. At Stone Initiatives, our trained experts are able to examine, identify and interpret mineralogical data to provide you with a clear insight into what applications are suitable for your stone.”
Ted Schmaal
Scientific Officer – Geologist
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Frequently asked questions
Can mineralogical examination identify what type of stone I have?
While XRD can provide a mineralogical breakdown of major components in the stone, it is not able to tell us the way the minerals look or spatially interact with one another. Petrographic analysis is the only way to truly identify the stone type of a chosen material. This is because true stone identification is based off both mineralogical composition and physical expression of those minerals in the sample. For example, limestones and marbles are both made of commonly made of calcite. Despite this, marble and limestone tend to have quite different physical characteristics and textural features.
Why would I need a mineralogical examination?
Mineralogical examinations are beneficial for any size of project that utilises natural stone. Whether you are looking to determine the quantity of crystalline silica in a product, testing a newly sourced or imported stone type for use in a project, or even testing manufactured materials for presence of asbestiform minerals, it is always valuable to truly understand the material you are working with.
What sample size is required for mineralogical examination?
Mineralogical examinations often only require a small quantity of sample, usually no more than a representative 100mm x 100mm piece. If the stone is highly variable, it may be useful to send several pieces to ensure the variation and important features of the stone are all captured.
How long does a mineralogical examination take?
Turnaround time is dependant on the type of analysis requested. Petrographic analysis has a turnaround time of 3-5 weeks due to the production time of the petrographic thin sections. XRD has a shorter turnaround time at only 1-3 weeks from sample receipt.
Can you test a material to determine if it is engineered stone?
Yes we can! Engineered stone in Australia is defined as an artificial product containing a minimum of 1% crystalline silica (often upwards of 90%), glass or other mineral aggregate material, mixed with water, resins or pigments and subsequently re-hardened. Testing if a material is considered engineered or natural stone comes down to determining the presence of both silica and resin in the samples. This can be achieved through a combination of XRD analysis to determine mineral phases present, followed by firing the dried, pulverised sample and recording any weight loss from the volatilization of potential resin compounds.
Can I request urgent testing?
Yes you can! There are many reasons why you may need an urgent mineralogical examination on your sample, such as providing a test certificate to the ABF for an inbound or held shipment. For an XRD analysis, a 2-5 day urgent turnaround time is possible. For petrographic analysis, an urgent turnaround time of 1-2 weeks is the minimum due to the production time of the petrographic thin sections.