Asbestos in dimension stone: The dangers and how to minimise risk

Asbestiform tremolite fibres

The use of asbestos has been banned in Australia since 2003, but did you know that it can be naturally present in dimension stone such as some marbles and granites? Whether you’re a stonemason, quarry person, builder or scientist in a lab, it’s vital that you know how to prevent exposure to these harmful asbestos fibres.

Article: Thomas Baggs

What makes asbestos dangerous?

Asbestos is a naturally occurring mineral fibre that comes from one of the many minerals known as Naturally Occurring Asbestos (NOA). These mineral fibres perform excellently as insulators, which is why they were mined and used in building materials for many decades. Unfortunately, they also pose a significant health hazard when in a respirable form and inhaled or ingested. The size, shape and longevity of the fibres make them particularly dangerous.

Size: When in a fibrous form, NOA can be broken into very tiny fibres that can become airborne. They are then able to be inhaled and can travel deep into the lungs, because the mucous in the lungs is not efficient at trapping tiny particles.

Shape: The tiny fibres are often thin and sharp. Once deep inside of the lungs, they can impale and penetrate the alveolar cells, creating scarring and triggering a severe immune response (inflammation).

Longevity: These fibres are relatively durable, and the body cannot break them down naturally. Therefore, the immune response to the invaded particles is usually unable to be resolved.

Continued exposure to these particles often leads to an accumulation of damaging fibres deep within the lungs, irritation, and a subsequent build-up of inflammation within the lungs (asbestosis). This run-away inflammation and cellular scarring are thought to be one cause of the formation of cancerous cells and in many cases the eventual development of mesothelioma. It is also possible that these fibres can make their way into other parts of the body, such as the stomach, and cause similar issues there.

It should be noted that development of an asbestos-related disease does not in all cases require continued fibre exposure. A short or even brief exposure to these particles can be enough to develop asbestos-related health issues.

Which stones can contain asbestos?

There are six main minerals that can form asbestiform fibres:

  • Tremolite
  • Actinolite
  • Chrysotile
  • Crocidolite
  • Amosite
  • Anthophyllite

For anyone working with dimension stone – whether at a quarry or mine site, in a laboratory, as a stone mason or in other related industries – knowing which minerals can be asbestiform is extremely important. All six of the minerals listed above can be present in dimension stone; however, the three types we encounter most often in the laboratory environment are tremolite, actinolite and chrysotile.

In a laboratory setting, tremolite is the NOA that we encounter most commonly. It is typically seen in white or green-coloured marbles. Actinolite is typically seen as an accessory or trace mineral in granitic, metamorphosed or mafic rock types that would typically be commercially classified as granites or black granites. Chrysotile belongs to the serpentine sub-group of minerals and as such is most commonly seen in serpentinites, typically commercially classified as green marbles.

Preventing exposure to asbestos in dimension stone

The NOA minerals listed above occur naturally alongside other minerals in a variety of different rocks, including stone quarried for dimension stone and rocks mined for mineral resources. It is of paramount importance that these airborne fibres are not encountered in the workplace. This can be achieved through prevention and protection methods.

Prevention method 1: Identification

An important first step in prevention is identifying the risk of a particular stone type and determining whether testing is advisable. There are certain types of stone that are more likely to contain NOA (e.g. marbles) and conversely, some types of stone that are less likely to contain NOA (e.g. sandstones). There are particular sub-types that come under the commercial definition of marble that may be of exceptionally high risk of containing NOA (e.g. serpentinite marbles).

Some moderate- to high-risk stone types (commercial classification) include:

  • Marble (particularly coloured white, green or blue; higher risk if veined)             
    • Serpentinite (occasionally classified into the marble commercial stone classification)
  • Granite (particularly if metamorphosed, altered or mafic in composition)

Lower-risk stone types (commercial classification) include:

  • Sandstone
  • Limestone and travertine

Realistically, any dimension stone could contain a trace quantity of NOA. However, in the dimension stone industry the most encountered stone types at higher risk of containing a large quantity of NOA are marbles, serpentinites, and other metamorphosed or altered stones. The next few figures show some photographic examples of dimension stone containing NOA.

Photograph of a piece of polished veined white marble.
Figure 1: Photograph of a piece of polished veined white marble. 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.
Photograph of a piece of polished veined white marble.
Figure 2: Photograph of a piece of polished veined white marble. This weakly magnified photograph shows a white-coloured stone with various opaque white, patterned veins and opaque grey-white patches with a fibrous appearance. The circled area is a patch of a fibrous-looking material that was found to be mostly comprised of tremolite. Many of the opaque white veins also contain a detectable quantity of tremolite. Features that are fibrous in appearance or opaque white veins can commonly contain NOA and are therefore worth looking out for when identifying NOA.
Photograph of a piece of polished 
'green marble serpentinite.
Figure 3: Photograph of a piece of polished ‘green marble’ serpentinite. This weakly magnified photograph shows a green-coloured stone with a white vein running through the middle (circled). This white vein contains chrysotile, which is NOA. Often, green marbles contain a high quantity of serpentine group minerals such as chrysotile. Features such as white veins or green-grey coloured veins are worth looking out for when distinguishing stone that may contain NOA.
Checklist: Identifying higher-risk stone types

When identifying stone types that are of higher risk, there are four main questions to consider.

  • Does the stone in question belong to a high-risk stone type category?
    e.g. marbles, serpentinites, dolomite marbles, metamorphosed granites, altered mafic stone.
  • Is there a fibrous texture?
    A fibrous texture or feature is the best indicator for the presence of asbestiform minerals.
  • Are there any patterning features such as veins?
    If it does not look plain or consistent, this suggests possible alteration or other metamorphic processes that can sometimes result in the formation of NOA minerals.
  • Are any of these features opaque white, green or blue?
    If yes, there is a possibility the feature contains an NOA mineral.
Prevention method 2: Testing

Once a high-risk stone type has been identified, the next step is getting the stone type tested specifically for the detection of NOA. The three main methods for this are an X-ray diffraction analysis to determine mineralogy (XRD), a petrographic examination, or a combined XRD and polarised light microscopy analysis. All methods involve disturbing the stone and should only be carried out in a controlled environment by an authorised laboratory. Stone Initiatives can facilitate testing for these methods, providing analysis to determine the presence and estimated quantity of NOA. Get in touch.

A standard X-ray diffraction analysis to determine mineralogy can be used as a screening test and is usually the first test carried out to determine if a sample contains any ‘larger than trace’ quantity of an NOA mineral. The sensitivity of this test on its own is somewhat limited.

A petrographic examination is a targeted analysis and generally used in conjunction with an XRD analysis to determine the distribution of any detected NOA in a sample, or explicitly identify the features in a stone that contain asbestiform minerals.

If NOA is strongly suspected or already detected by one of the above analyses, a more sensitive method involving both X-ray diffraction analysis and polarised light microscopy is recommended to determine the presence of any trace quantities of NOA or to specifically classify the presence, type and relative quantity of asbestiform fibres.

Photomicrograph of a cluster of asbestiform chrysotile fibres intermixed with other various minerals.
Figure 4: 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. This was a sample taken from a white vein in a ‘green marble’ serpentinite. The elongate, fibre-like structure of the mineral is obvious in this view.
Prevention method 3: Inhibiting release of fibres

Inhibiting the release of fibres can be easily achieved by not disturbing any stone that contains NOA to the point where fibres may be released. This involves but is not limited to:

  • avoiding cutting, abrading, drilling of the stone
  • avoiding over-handling the stone (i.e. rubbing)
  • avoiding breaking or dropping the stone.

Depending on the quantity of NOA minerals identified in a particular stone type, this may mean that the stone is unsafe to be used in service, or in some cases even unsafe to transport. It is generally unsafe to process stone that contains NOA into smaller blocks, panels or tiles.

Protection methods

Once all preventative measures have been exhausted, there is still a chance that trace quantities of NOA minerals will slip through undetected and therefore unmitigated. It is therefore of paramount importance that protection measures are put in place to reduce incidental exposure to the particles when handling dimension stone.

Some approaches for this include:

  • Personal Protective Equipment (PPE), such as a P2 face mask, should be worn whenever cutting, drilling or abrading any dimension stone.
  • More extensive PPE such as overalls, gloves or other body protection may be considered for higher risk stone types.
  • Employing the use of wet cutting practices only and never dry cutting.
  • Ensuring there is adequate ventilation in stone processing environments.
  • Keeping work areas clean and dust-free.

Many other protection methods can also be used, depending on workplace conditions such as the types of stone being processed, and the practices employed for processing.

Staying safe – main points

The size, shape and longevity of asbestiform fibres makes them extremely dangerous to our health. The fibres are released when Naturally Occurring Asbestos (NOA) minerals are disturbed. These minerals can be found in a wide range of common dimension stone products, including rock types commercially classified as granites and marbles. It is vital that appropriate prevention and protection practices (including testing) are carried out to help reduce the risk of exposure.

For asbestos/NOA enquiries email Thomas Baggs at tbaggs@stonemtg.com.au

Note: The Australian Border Force has strict prohibitions regarding the import of materials that contain asbestos into Australia – this includes any dimension stone products containing NOA. More information on import restrictions and penalties can be found at http://www.abf.gov.au/asbestos
Disclaimer: This article is for informational purposes only. It is not intended to be a substitute for professional medical advice. Always seek the guidance of your doctor or other qualified health professional with any questions you may have regarding your health or a medical condition. 

Sources:

  1. Asbestos Awareness Campaign. Naturally Occurring Asbestos (NOA). Retrieved 29/6/2021.
  2. NSW Health. Asbestos and health risks. 11 August 2017. Retrieved 1/7/2021.
  3. Australian Border Force. Asbestos. 12 March 2021. Retrieved 1/7/2021
  4. Australian Government DHA. Asbestos – changes to the Customs (Prohibited Imports) Regulations 1956. 26 March 2019. Retrieved 1/7/2021.
  5. World Health Organisation. Asbestos: elimination of asbestos-related diseases. 15 February 2018. Retrieved 2/7/2021.
  6. ASTM International Standards (2020), Standard Terminology Relating to Dimension Stone, ASTM C119 – 2020, ASTM International, PA, USA.
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