The Fundamental Hardness Difference
| Material | Mohs Hardness | Composition | Character |
|---|---|---|---|
| Marble | 3-5 | Calcium carbonate (CaCO₃) | Soft, brittle, reacts with acid |
| Granite | 6-7 | Quartz + feldspar | Hard, brittle, no reaction with acid |
| Travertine | 3-4 | Calcium carbonate (porous) | Marble-like but more brittle |
| Onyx | 6-7 | A quartz variant | Translucent, decorative |
| Quartzite | 7 | Quartz dominant | Very hard, harder going than granite |
| Engineered stone | ~7 | Quartz + resin | Man-made; as hard as granite |
Mohs is an ordinal scale — the steps are not linear. Between 6 and 7 the real abrasion resistance rises by a factor of two to three, so granite machines two to three times "harder" than marble.
Cutting Speed Compared
| Parameter | Marble | Granite |
|---|---|---|
| Blade diameter (recommended) | 350-400 mm | 350-400 mm |
| Blade speed | 2,500-3,500 rpm | 2,000-3,000 rpm |
| Feed rate | 1,500-3,000 mm/min | 500-1,500 mm/min |
| Depth of cut per pass | 50-100 mm | 30-60 mm |
| Tool life (linear) | 300-500 m | 80-150 m |
| Water flow | 20-30 L/min | 30-45 L/min |
| Spindle load | Low to medium | Medium to high |
Practical Tip
Cutting granite is 50-70% slower than cutting marble. If the same project mixes granite and marble, allow for that when you programme the machine — set aside separate time blocks for the granite parts.
Diamond Blade Selection — For Marble
- Mesh: #50-60 (medium grit)
- Bond: soft to medium (marble is soft → the diamond must be exposed quickly)
- Segment height: 8-10 mm
- Segment count: 16-24
- Typical life: 300-500 m of linear cutting
Diamond Blade Selection — For Granite
- Mesh: #40-50 (coarser grit)
- Bond: medium to hard (granite is hard → the bond has to hold its hardness too)
- Segment height: 10-12 mm (thicker)
- Segment count: 16-20
- Typical life: 80-150 m of linear cutting (30% of marble)
What a Wrong Blade Does
A hard bond and coarse mesh blade used on marble behaves as if it were on granite — the diamond does not wear, you get a bright surface but the cut stalls. A soft bond on granite → the diamond sheds quickly and tool life is very short.
Cooling Water — The Marble and Granite Difference
- Marble: 20-30 L/min is enough (soft material, little heat)
- Granite: 30-45 L/min is essential (hard material, far more heat)
- Water temperature: 20-25°C is ideal (a chiller is needed in the summer months)
- Marble and acid: the cutting water can be neutralised with vinegar (marble reacts with excessively acidic water)
- Granite and water: a neutral pH is sufficient
What to Expect from the Surface Quality
The Marble Cut Face
- A matt surface, easily worked
- Polished afterwards on a polishing machine
- Cutting faults are easy to see with the naked eye
- A higher risk of cracking (brittle)
- Thin material (≤30 mm) demands great care
The Granite Cut Face
- Matt but a tight surface
- Polishing is harder — precision tooling is needed
- Micro-cracks are rarely seen
- Very robust; thick work is straightforward
- Heterogeneous colour (granite) → the cut line can be conspicuous
Post-Cutting Operations
- MARBLE: a smooth polish takes 5-7 grit steps (60 → 200 → 400 → 800 → 1500 → polishing powder)
- GRANITE: 7-10 grit steps (a denser structure, so more stages)
- EDGE rounding: can be done in a single setup on a 5-axis CNC
- V-CUT (45° chamfer): five axes are essential; the job is difficult on four
- Sink cut-outs — easy in marble; a long job in granite
- Corner cuts: on granite watch the engagement angle carefully (micro-cracking)
Advice for a Mixed-Production Workshop
Practical advice for workshops that cut both marble and granite:
- Keep two separate blade sets ready (marble + granite) and do not mix them
- A blade change takes 2 minutes — build a "blade change" pause into the programme
- Granite first, marble second (granite dust can dirty marble)
- The water circuits can be kept separate; granite water is changed more often (stone dust build-up)
- Operator training — the parameters for both materials should be known by heart