# Garnet abrasive

Natural garnet abrasive identity, producer-specific mineral and oxide analyses, particle form, sieve distributions, density, and the limits of blasting and waterjet grade claims.

Reviewed: 2026-10-29

Tags: abrasives, garnet, abrasive-grains

## Identity and scope

GMA’s Australian **ClassicCut 80** sheet gives **36% SiO₂** in its oxide analysis and identifies that silica as lattice-bound. The same sheet reports **less than 0.1% quartz** and **more than 96% almandine garnet** in its typical mineral analysis. The oxide and mineral columns answer different composition questions. [GMA ClassicCut 80 APAC PDS](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/APAC/PDS%20-%20GMA%20ClassicCut%2080%20apac-en.pdf) Almandine is one of several garnet end members. [Geoscience Australia, Garnet, updated 14 May 2025](https://www.ga.gov.au/education/minerals-energy/australian-mineral-facts/garnet)

The almandine end member is Fe²⁺₃Al₂(SiO₄)₃. The mineral handbook lists cubic structure, brittle tenacity, subconchoidal fracture and Mohs 7–7.5. Supplier grades have their own mineral mixtures and particle distributions. [Mineralogical Society of America, almandine entry](https://www.handbookofmineralogy.org/pdfs/almandine.pdf)

This reference covers abrasive grains. A named supplier grade adds a mineral assemblage, particle distribution, processing history, and quality basis. Synthesis is that the word "garnet" alone leaves those attributes unresolved. A coated abrasive containing garnet also has a backing and bond, which are outside this grain reference.

## Deposits, processing, and particle form

Garnet occurs in metamorphic and igneous rocks and can persist in weathered sediment. Geoscience Australia describes river transport to the Port Gregory sand deposit. Its processing account distinguishes wet separation and washing from drying, magnetic separation, and screen grading. These are examples of production stages, not a universal treatment specification. [Geoscience Australia, formation, resources, and processing](https://www.ga.gov.au/education/minerals-energy/australian-mineral-facts/garnet).

Alluvial, river, beach, and hard-rock descriptions concern deposit or production origin. GMA describes its Australian and South African garnet history through weathering, floodplains, offshore transport, and shore deposition. The same page describes sub-angular grains. Those statements concern GMA's described material. [GMA, Our garnet, alluvial history](https://gmagarnet.com/en/our-garnet).

GMA's Americas ExcelCut page describes crushed hard-rock almandine with sharp, angular particles. However, its ExcelCut 120 sheet identified below calls the natural grain shape sub-angular. The documents differ in scope and age. Neither description supplies a measured angularity distribution or resolves the other document's wording. [GMA ExcelCut product page](https://gmagarnet.com/en/americas/waterjet/excelcut), [GMA ExcelCut 120 PDS, V1-2018-08](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/Americas/PDS%20-%20GMA%20ExcelCut%20120%20us-en.pdf).

Synthesis is that geological origin, crushing, washing, separation, and grading describe different attributes. Origin alone cannot establish finished grain shape, cleanliness, or process performance. The reviewed sheets do not establish a universal coating or chemical-treatment state.

## Mineral composition differs from oxide analysis

BARTON's ADIRONDACK HPX sheet dated 2021-01 reports 92–96% garnet comprising almandine, pyrope, and grossular. It groups magnetite, hornblende, feldspar, mica, and other minerals at 4–8%. It warns that this natural product's chemical analysis varies. The sheet does not give individual garnet end-member percentages or a mineral-analysis method. [BARTON, HPX technical data](https://www.barton.com/wp-content/uploads/2021/04/Technical-Data-ADIRONDACK-HPX.pdf).

GMA's Australian ClassicCut 80 sheet, code `GMA-AUS 80 – V1-2020`, reports typical oxide composition. [GMA ClassicCut 80 APAC PDS](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/APAC/PDS%20-%20GMA%20ClassicCut%2080%20apac-en.pdf).

| Reported oxide | Typical percentage |
| --- | --- |
| SiO₂ | 36% |
| Al₂O₃ | 20% |
| FeO | 30% |
| Fe₂O₃ | 2% |
| MgO | 6% |
| CaO | 2% |
| TiO₂ | 3% |
| MnO | 1% |

Its SiO₂ footnote specifies lattice-bound silica. Typical mineral content is predominantly almandine garnet above 96% and quartz below 0.1%. The chemistry table does not explicitly label a mass-fraction basis. [GMA ClassicCut 80 APAC PDS, composition and footnote](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/APAC/PDS%20-%20GMA%20ClassicCut%2080%20apac-en.pdf).

The American ExcelCut 120 sheet, code `GMA-USA-120 PDS-V1-2018-08`, instead reports typical garnet content of 89%, hornblende 6%, and pyroxene 3%. Its typical oxide table gives FeO as `NA` and Fe₂O₃ as 36%. `NA` is not a measured zero. [GMA ExcelCut 120 PDS, composition](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/Americas/PDS%20-%20GMA%20ExcelCut%20120%20us-en.pdf).

Synthesis from these separate tables is that oxide analysis and mineral percentages answer different questions. Reported SiO₂ cannot be substituted for free crystalline quartz content. An iron-oxide entry cannot be substituted for free metallic iron. Neither a mineral formula nor a bulk analysis proves an iron-free product, a contamination limit, or a particular assay method. Typical analyses are not guaranteed lot acceptance limits.

## Hardness, fracture, and density

HPX lists sharp, angular, irregular grains, Mohs hardness 7.5–8.5, and a qualitative strength description ranging from friable to tough. It labels 3.9–4.1 g/cm³ as specific gravity. That label carries density units in the original sheet. [BARTON, HPX physical properties](https://www.barton.com/wp-content/uploads/2021/04/Technical-Data-ADIRONDACK-HPX.pdf).

ClassicCut 80 lists typical bulk density 2.3 T/m³, specific gravity 4.1, and hardness 7.0–8.0 Mohs, without a packing procedure. [GMA ClassicCut 80 APAC PDS, physical characteristics](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/APAC/PDS%20-%20GMA%20ClassicCut%2080%20apac-en.pdf).

Synthesis is that specific gravity, a dimensionless density ratio, differs from solid density expressed as mass per solid volume. Bulk density includes the space between grains and depends on packing. The reported bulk value cannot be treated as a tapped or loose-pack test result without its method. Mohs hardness, qualitative friability, and particle shape describe different properties. The mineral handbook and supplier ranges remain separate evidence rather than one universal garnet hardness range.

For an illustrative calculation, assume the reported bulk density applies unchanged. One tonne equals 1,000 kg. The derived volume of 1,000 kg is 1,000 kg ÷ 2,300 kg/m³ ≈ 0.435 m³. Packing remains an assumption, not a measured package volume or usable hopper capacity.

## Mesh labels and particle distributions

ClassicCut 80 gives typical weight retention at mesh 60, aperture 250 µm, as 55% cumulative and 32% discrete. At mesh 80, aperture 180 µm, values are 92% and 14%. No sieve-series standard or edition is named. [GMA ClassicCut 80 APAC PDS, product range](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/APAC/PDS%20-%20GMA%20ClassicCut%2080%20apac-en.pdf).

ExcelCut 120's whole-percent Cumulative and Discrete columns do not reconcile exactly as printed. At 150 µm, cumulative retention rises from 45% to 85%, while discrete retention is 39%. Its discrete column sums to 101%, and the pan row gives 1% despite unchanged cumulative retention of 100%. [GMA ExcelCut 120 PDS, typical weight-retained table](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/Americas/PDS%20-%20GMA%20ExcelCut%20120%20us-en.pdf). Conditional mathematical synthesis is that independent rounding of each column to whole percentages can produce all these entries from one valid underlying distribution totaling 100%. The printed sums and differences therefore do not establish an invalid distribution. The sheet supplies neither unrounded measurements nor a rounding policy, so this possibility does not identify the supplier's actual measurements or reporting method. These typical values are not lot limits.

Synthesis is that cumulative retention includes material on the stated sieve and coarser sieves. Discrete retention describes one fraction. A mesh grade is not one particle diameter, a median, or a finished-surface roughness. One millimetre equals 1,000 µm. Neither reviewed mesh label establishes a FEPA F or P designation or an automatic conversion to another supplier's grade.

## Blast-cleaning standards and application limits

ISO 11126-10:2025, edition 3 dated November 2025, supersedes the 2017 edition. Its public abstract covers almandite garnet supplied new for blast cleaning. The scope identifies particle size, apparent density, Mohs hardness, moisture, aqueous-extract conductivity, and water-soluble chlorides. Test methods belong to the ISO 11127 series. The requirements exclude abrasive during or after use. [ISO, 11126-10:2025 edition record and abstract](https://www.iso.org/standard/88989.html).

Only the publisher's public scope and edition record support this standards summary. The paid normative acceptance tables were not reviewed. This article therefore makes no ISO conformity claim for any named product. The scope does not qualify waterjet performance or reused media.

GMA markets ExcelCut for waterjet cutting and lists stone, glass, aerospace, automotive, and defense applications. Those are producer product-family statements. They do not establish compatibility with every workpiece or an achieved finish. [GMA ExcelCut, industry applications](https://gmagarnet.com/en/americas/waterjet/excelcut).

## Safety evidence and coverage limits

GMA's ExcelCut 50 SDS issued 3 August 2018 reports quartz below 0.2% by weight. It classifies the product under US HCS 2012 as Carcinogenicity 1A and warns about inhalation of respirable crystalline-silica dust. Its disposal section distinguishes supplied material from material contaminated or reduced to dust in use. This historical SDS is for ExcelCut 50, not the 120 grade's composition certificate. [GMA ExcelCut 50 SDS, sections 2, 3, 11, and 13](https://gmagarnet.com/hubfs/Resources/Waterjet%20Cutting/Data%20sheets/Americas/SDS%20-%20GMA%20ExcelCut%2050%20GMX%20us-en.pdf).

Synthesis is that a low reported quartz percentage does not mean zero silica or safe airborne exposure. The 2018 document does not establish current regulatory exposure limits. Its supplied-product descriptions do not prove environmental harmlessness after use. Safety information is separate from cutting performance.

The source set comprises the dated sheets identified above, the 2001 mineral entry, Geoscience Australia's 2025 page, undated GMA pages accessed on the reviewed date, and the public ISO edition record. No lot certificates, current agreed purchase specifications, or comparative process experiments were available in this source set. The GMA sheets do not identify individual test-method numbers or editions. The ExcelCut 120 sheet mentions ISO and ASTM testing without resolving those methods.

No universal operating pressure, nozzle geometry, feed rate, consumption, reuse count, cutting rate, achieved finish, or customer capability follows from these references. Product-specific recycling or productivity claims need their own material, equipment, recovery, and test conditions. Commercial grade names leave those process conditions unresolved.

## Related references

- [Black silicon carbide abrasive](black-silicon-carbide-abrasive.md).
- [Finishing process references](../../processes/finishing/index.md).