Slate & Quartzite — Complete Guide
Slate and quartzite are two closely related metamorphic rocks that have become highly sought-after natural stones for cladding, flooring, roofing and landscaping. Both are formed when sedimentary parents (shale for slate, sandstone for quartzite) are subjected to heat and pressure inside the earth.
India is one of the world’s largest exporters of slate (from Andhra Pradesh, Madhya Pradesh, Himachal Pradesh) and quartzite (from Rajasthan, Karnataka, Madhya Pradesh). They are governed by IS 1124, IS 1121, IS 4101, IS 14223 (Part 4).
What is Slate?
Slate is a fine-grained, foliated metamorphic rock formed when shale or clay sediments are subjected to low-grade metamorphism. The rock develops a strong “slaty cleavage” that allows it to split into thin, flat sheets — perfect for natural roofing tiles, floor pavers, wall cladding and blackboards.
Slate is naturally water-impermeable, fire-resistant, frost-resistant and has a lifespan of 75–200 years as a roofing material — making it one of the longest-lasting natural building materials known.
What is Quartzite?
Quartzite is an extremely hard, dense metamorphic rock formed when quartz-rich sandstone is subjected to high temperature and pressure. The quartz grains recrystallise and fuse, producing a stone that is harder than granite (Mohs 7), nearly waterproof and resistant to almost all chemicals.
Quartzite is often confused with quartz countertops — but those are engineered (man-made), while quartzite is 100% natural stone. True quartzite scratches glass but is not scratched by knife steel.
Composition
Slate
| Constituent | Percentage |
|---|
| Quartz | 30 – 45% |
| Mica (Muscovite, Chlorite) | 20 – 30% |
| Feldspar | 10 – 20% |
| Clay minerals | 10 – 15% |
| Iron Oxides / Carbonaceous matter | 5 – 10% (colour) |
Quartzite
| Constituent | Percentage |
|---|
| Quartz (SiO₂) | 90 – 99% |
| Feldspar | 1 – 5% |
| Mica | 0 – 3% |
| Iron Oxide | 0 – 4% (red, brown, pink tints) |
| Other accessory minerals | < 2% |
Popular Indian Varieties
Slate
| Variety | Colour | Origin |
|---|
| Multicolour Slate | Red / brown / green / silver | Madhya Pradesh, Andhra |
| Jak Black | Solid black | Andhra Pradesh |
| Jak Black Riven | Black with split-face texture | Andhra Pradesh |
| California Gold | Yellow-gold tones | Madhya Pradesh |
| Copper Slate | Copper-bronze | Andhra Pradesh |
| Indian Autumn | Autumn red-brown | Madhya Pradesh |
| Indian Rustic | Mixed warm colours | Madhya Pradesh |
| Himachal Slate | Grey-blue | Himachal Pradesh (roofing) |
Quartzite
| Variety | Colour | Origin |
|---|
| Silver Sparkle | Silver with mica sparkle | Rajasthan |
| Desert Mint | Pale green | Rajasthan |
| Copper Quartzite | Copper-bronze | Rajasthan |
| Indus Gold | Yellow / golden | Madhya Pradesh |
| Himalayan Black | Black with white veins | Madhya Pradesh |
| Tandur Yellow | Yellow | Telangana |
Standard Sizes & Forms
| Form | Typical Size | Thickness |
|---|
| Slate Roof Tile | 300 x 200 / 400 x 200 mm | 5 – 10 mm |
| Slate / Quartzite Floor Tile | 300 x 300 / 600 x 300 / 600 x 600 mm | 10 – 25 mm |
| Cladding Strip | 50–200 mm wide x random length | 10 – 30 mm |
| Random / Crazy | Random | 15 – 30 mm |
| Mosaic / Cobble | 50–100 mm pieces | 10 – 30 mm |
| Stacked Stone Panel | 600 x 150 / 600 x 200 mm | 15 – 40 mm (variable) |
Physical & Mechanical Properties
| Property | Slate | Quartzite |
|---|
| Density | 2,600 – 2,900 kg/m³ | 2,600 – 2,800 kg/m³ |
| Compressive Strength | 100 – 200 MPa | 200 – 400 MPa |
| Flexural Strength | 40 – 80 MPa | 15 – 25 MPa |
| Water Absorption | 0.1 – 0.4% | 0.1 – 0.5% |
| Mohs Hardness | 3 – 5 | 7 |
| Abrasion Resistance | Good | Excellent |
| Slip Resistance (cleft) | Excellent | Excellent |
| Frost Resistance | Excellent | Excellent |
| UV / Colour-Fastness | Excellent | Excellent |
| Thermal Conductivity | 1.8 – 2.5 W/m.K | 3.0 – 5.5 W/m.K |
| Acid Resistance | Excellent | Excellent |
Surface Finishes
- Natural / Riven / Cleft: Original split surface — most popular look
- Honed: Smooth matt finish
- Polished: Glossy mirror finish (quartzite only — slate’s mica matrix limits polish)
- Calibrated: Uniform thickness for tile installation
- Brushed / Antique: Soft worn texture
- Sandblasted: Anti-slip rough texture
- Flamed: Coarse heat-treated surface (quartzite)
- Stacked / Ledge: Cut into strips for dry-stack cladding panels
Tests on Slate & Quartzite
- Compressive Strength — IS 1121 (Part 1)
- Flexural Strength — IS 1121 (Part 2)
- Water Absorption & Specific Gravity — IS 1124
- Abrasion Resistance — IS 1706
- Frost / Durability — IS 1126
- Petrographic Analysis
- Mohs Hardness
- Acid Resistance Test
- Cleavage Plane Test (slate)
- Roofing Soundness Test (slate — BS EN 12326)
Slate vs Quartzite vs Granite — Comparison
| Parameter | Slate | Quartzite | Granite |
|---|
| Rock Type | Foliated metamorphic | Metamorphic (silica) | Igneous |
| Mohs Hardness | 3 – 5 | 7 | 6 – 7 |
| Compressive Strength | 100 – 200 MPa | 200 – 400 MPa | 100 – 250 MPa |
| Water Absorption | 0.1 – 0.4% | 0.1 – 0.5% | < 0.5% |
| Acid Resistance | Excellent | Excellent | Excellent |
| Polish | Limited (riven look) | Glossy | Glossy |
| Roofing Use | Excellent | Limited | Limited |
| Cost (Rs/sqft) | 40 – 200 | 80 – 400 | 80 – 350 |
| Best for | Roofing, rustic cladding | Premium counter, cladding | Floors, kitchen counter |
Uses
Slate
- Natural roof tiles (sloped roofs)
- External wall cladding (riven, stacked)
- Internal feature walls (rustic decor)
- Garden paving and stepping stones
- Pool deck and step coping
- Fireplace surrounds and hearths
- Mosaic and pebble art
- Boundary wall capping
- Decorative landscaping (slate chips)
- Blackboards / billiards table tops (historical)
- Window sills and lintels
Quartzite
- Kitchen platforms / countertops (premium)
- Polished flooring (luxury homes, hotels)
- External and internal wall cladding
- Pool decks and step copings (slip-resistant)
- Industrial / heavy-duty flooring
- Wash basin and bathroom vanity tops
- Feature walls and accent panels
- Outdoor paving (sparkle finish)
- Boundary wall capping
- Stacked stone cladding panels
- Garden landscaping (premium look)
Advantages
- Both stones have very low water absorption (<0.5%)
- Excellent slip resistance with natural riven / cleft finish
- Highly weather-resistant — UV stable, frost-proof
- Acid and stain resistant
- Fire-resistant (good for fireplaces, kitchens)
- Eco-friendly — natural, recyclable
- Slate: 75–200 year roof lifespan (longest of any roofing)
- Quartzite: harder than granite — ideal for high-use applications
- Beautiful natural patterns — every slab unique
- Wide variety of warm earthy colours and tones
- Slate splits naturally — minimal cutting waste
- Both stones add premium / heritage value to property
- Hygienic and non-porous when sealed
Disadvantages
- Slate is brittle — chips/breaks if dropped or hit hard
- Slate roofing requires specialised carpenters / fitters
- Quartzite is very hard to cut — diamond tools required
- Both stones heavy — need strong substrate / roof structure
- Quartzite cost is higher than basic granite
- Slate’s natural cleft creates uneven thickness — difficult installation
- Joints can collect dirt if not properly grouted
- Cold underfoot in winter
- Slate roofs need proper underlayment — cannot be installed on weak structures
- Slip risk on polished quartzite when wet
- Limited colour fastness in some lower-grade slates (fading over decades)
- Some slate varieties contain iron pyrites which rust over years
Quantity Estimation
| Application | Wastage |
|---|
| Slate roofing tiles | 10 – 15% |
| Plain floor / cladding | 8 – 10% |
| Crazy / random paving | 15 – 20% |
| Stacked stone panels | 10 – 15% |
| Quartzite countertops | 15 – 25% |
| Mosaic / pebble | 15 – 25% |
Required Area = Net Area × (1 + Wastage %)
Best Practices for Installation
Slate Roofing
- Use only Grade 1 slate (low absorption, no iron pyrites)
- Roof pitch minimum 25° for slate tiles
- Lap each course minimum 75–100 mm
- Fix with stainless steel / copper nails (never mild steel — rusts)
- Always provide breathable underlayment
- Check each tile by “ringing” (tap test — clear ring = sound; dull = cracked)
Slate / Quartzite Cladding & Flooring
- Use 1:4 cement-sand mortar bed (20–25 mm) for floors
- Use polymer-modified tile adhesive for vertical cladding
- For cleft / riven, calibrate the backside for uniform mortar contact
- Maintain 3–5 mm joints, fill with colour-matched grout
- Apply penetrating sealer (silicone / fluoropolymer) before grouting
- Re-seal every 1–3 years in exposed outdoor applications
- Use stainless steel fixings only
- For stacked stone panels, mechanical anchors recommended above 1.5 m height
- Avoid acidic / alkaline cleaners — use pH-neutral stone cleaner
Cost (Approximate, Indian Market)
Slate
| Variety / Form | Rate (Rs / sqft) |
|---|
| Multicolour Slate Tile | 40 – 80 |
| Jak Black / Copper Slate | 60 – 120 |
| California Gold / Indian Autumn | 80 – 160 |
| Slate Roofing Tile | 120 – 250 |
| Stacked Slate Panel | 100 – 250 |
Quartzite
| Variety / Form | Rate (Rs / sqft) |
|---|
| Silver Sparkle / Desert Mint | 80 – 150 |
| Copper / Tandur Yellow | 100 – 200 |
| Polished Quartzite Slab | 180 – 400 |
| Premium designer / imported | 400 – 1,200+ |
| Installation labour | 50 – 100 / sqft |
| Sealing & finishing | 20 – 40 / sqft |
Applicable Standards
| Standard | Description |
|---|
| IS 1124 | Water absorption, specific gravity and porosity of natural building stones |
| IS 1121 (Parts 1–4) | Strength test methods for natural building stones |
| IS 1126 | Durability of natural building stones |
| IS 1706 | Abrasion resistance |
| IS 4101 (Part 1) | External facing and veneering — stone facing |
| IS 14223 (Part 4) | Polished building stones — Slate & Quartzite Specification |
| IS 1597 | Code of practice for construction of stone masonry |
| BS EN 12326 | Slate and stone for discontinuous roofing and external cladding |
Conclusion
Slate and quartzite represent the two extremes of the metamorphic stone family — one prized for its perfect cleavage and roofing durability, the other for its extreme hardness and luxurious polish.
For natural slate roofing (hill stations, heritage homes, eco-villas), the longevity of slate is unmatched — a slate roof can outlast its building. For premium kitchen countertops, polished feature walls and high-end flooring, quartzite outperforms granite in hardness while offering more dramatic patterns. For rustic cladding and garden landscapes, riven slate offers warm earthy character.
If you want softer colours and easier carving, look at sandstone or Jaisalmer Stone; for affordable utility flooring, see Kota or Kadappa Stone; for the gold standard premium look, choose granite or marble.