Onyx is a natural stone in which minerals deposited layer upon layer form fine, parallel bands. In interior architecture and the stone trade, onyx means banded, translucent calcite deposited from spring or cave waters; in mineralogy, however, the same name is given to banded chalcedony from the quartz family. The stone used in lamps, the one that lets light pass through it, is calcite onyx.
In this guide you will find how onyx stone forms, the two different definitions of onyx, the characteristics that set onyx apart from marble, its hardness, and its five main colors.
How does onyx stone form?
Onyx forms when water rich in calcium carbonate leaves behind, very slowly, the mineral it carries. Each new layer is deposited on top of the previous one; over time the stone becomes a dense mass woven from fine bands.
The process begins with groundwater seeping through limestone. Water containing carbon dioxide dissolves the limestone and carries calcium carbonate in solution. When this water rises to the surface at a spring or reaches a cave cavity, it loses its carbon dioxide, and the calcium carbonate precipitates again as calcite crystals. Stalactites and stalagmites in caves grow by the same chemistry.
Each band records the state of the water at that time. When the flow rate or the amount of elements such as iron carried by the water changes, the color and density of the layer change too. The honey, red, and cream stripes you see on a polished onyx surface are traces of these changes, accumulated over thousands of years.
What is onyx marble, and is it really marble?
Onyx marble is the stone trade’s commercial name for banded calcite onyx; in the geological sense, it is not marble. Because most carbonate stones that take a polish are called marble in the trade, onyx is often sold under this name too.
True marble is a metamorphic rock formed when limestone recrystallizes deep underground under heat and pressure. Onyx never goes through this stage; it is a sedimentary stone precipitated directly from water. In this respect it is closer to the travertine family: both are calcite precipitated from spring waters, but onyx is much denser, less porous, and translucent.
Is onyx in mineralogy the same stone as onyx in interior design?
No, there are two separate materials that bear the same name. The stone mineralogists call onyx is parallel-banded chalcedony from the quartz family; interior architects and stonemasons, by contrast, use the name for banded calcite.
Chalcedony onyx, whose name derives from the Greek word for fingernail, forms when siliceous solutions are deposited layer by layer in rock cavities. It is recognized by its sharp black-and-white or red-and-white bands; because it is hard and dense, it is used in jewelry, relief carving, and small objects. Calcite onyx, on the other hand, is quarried in large blocks, is easier to work, and lets light pass through it.
This confusion goes back a long way. Most of the stone used to make vessels and jars in ancient Egypt, known today as Egyptian alabaster, is in fact banded calcite as well. The table below shows the three materials side by side.
| Property | Calcite onyx (onyx marble) | Marble | Chalcedony onyx |
|---|---|---|---|
| Mineral | Calcite (calcium carbonate) | Calcite and/or dolomite | Chalcedony (silicon dioxide, quartz family) |
| Formation | Precipitation from spring and cave waters (sedimentary) | Transformation of limestone by heat and pressure (metamorphic) | Precipitation from siliceous solutions in rock cavities |
| Pattern | Parallel or wavy bands | Irregular veins, cloudy ground | Sharp, straight, parallel bands |
| Light transmission | Translucent; transmits light even at a thickness of 1–2 cm | Practically opaque unless cut very thin | Limited; varies with the color of the band |
| Hardness (Mohs) | About 3 | About 3–4 | About 6.5–7 |
| Typical use | Lighting, backlit panels, bar counters, objects | Floors, countertops, cladding, sculpture | Jewelry, relief carving, small objects |
Why does onyx let light through?
Onyx is translucent because it is made of slowly grown, orderly calcite crystals and contains few impurities that block light. Instead of bouncing back from the surface, light travels onward, scattering between the crystals, and emerges from the other side of the stone as a soft glow.
This translucency is not the same in every band. Light bands of pure calcite let light through generously, while darker bands containing iron or clay let less through. That is why the pattern deepens when the lamp is lit: because the bands glow at different intensities, the surface looks like a layered painting. A solid sculpture when unlit, the stone becomes a stained-glass window when lit, its veins appearing one by one.
Thickness is decisive too. In Nyxora lamps, the stone is reduced to a wall thickness of 6–12 mm depending on the model and the light source; this range is thin enough to let light through and thick enough to withstand daily use. We covered the physics in detail in our article on why onyx lets light pass through it.
How can you tell onyx from marble?
The quickest way is to hold the stone up to light: onyx lets light pass through and illuminates its bands, while marble largely reflects light from its surface. Even without light, you can tell them apart by looking at the pattern, the depth, and the hardness.
- Pattern: In marble, the veins are irregular and often scatter across the ground as broken lines. The bands of onyx, by contrast, are layers that follow one another in parallel or wavy lines.
- Depth: When you look at the surface of polished onyx, the pattern seems to come from a few millimeters inside; in marble, the pattern sits on the surface.
- Hardness: Onyx is around 3 on the Mohs scale; it is softer and more fragile than marble. That is why it is chosen for walls, objects, and lighting rather than for high-traffic floors.
- Chemical sensitivity: Both are carbonate stones. Vinegar, lemon juice, and acidic cleaners can permanently dull either surface.
To tell onyx from resin, glass, and printed imitations, see the checks that do not harm the stone in our guide on how to tell if onyx is real.
Where is onyx used?
Calcite onyx is a stone that reveals its character when used with light; that is why you most often find it on backlit surfaces and in lighting objects. Backlit wall panels, the fronts of bar and reception counters, lamps, vases, and small decorative objects are its main uses.
Because of its softness and sensitivity to acids, it is less often chosen for heavily used kitchen countertops and high-traffic floors. A lamp, on the other hand, is a natural use for the stone: an object that is not exposed to frequent wear, and one in which light makes the stone visible anew every evening.
How durable is onyx in everyday use?
Onyx poses no problems in everyday use; however, it should be protected from impacts, falls, and acidic substances. The softness that makes the stone easy for artisans to work simply asks for a little care from the person who uses it.
There is little to watch for with an onyx lamp: place it on a flat, stable surface, keep it away from direct sunlight, and wipe the surface with a soft, dry microfiber cloth instead of liquid cleaners, solvents, or abrasives. Unplugging the lamp and waiting for the bulb to cool when you change it is for your safety and the stone’s. For a detailed routine, see our onyx lamp care guide.
An LED bulb is recommended as the light source because it produces little heat. For color temperature, 2700 K warm white is preferred; cool white light fades the stone’s color gradations and turns them gray.
What colors does onyx come in?
The color of onyx comes from the minerals carried by the water during deposition. Pure calcite is colorless or white; iron oxides produce honey, orange, red, and brown tones. Green and pink onyx also occur in nature.
The five onyx types presented on Nyxora’s Material page can be summarized by their relationship with light as follows:
- Honey onyx: A crystalline, translucent body produced by slow deposition; when lit, it turns a warm amber. Brime d’Onyx is carved from this stone.
- Blue onyx: A rare type; it carries rust-colored veins left by iron oxides on a gray-blue ground. In light, cool blue and warm copper meet on the same surface; Ombrelle d’Onyx is an example.
- River onyx: Reddish-brown and cream bands that flow in waves, recalling river sediment; in light, they turn amber and copper. Strata d’Onyx uses this stone as a horizontal block.
- Orange onyx: Warm yellow-orange bands interrupted by gray-blue transitions; lit, it recalls a sunset, and unlit, a sculpture with a sedimentary texture. Halo d’Onyx is made entirely of this stone.
- White onyx: The type with the highest light transmission; it carries fine honey and gray lines on a milk-white ground and glows almost like glass when lit. Luma Curve d’Onyx is an example of this stone.
We compared in detail how the colors change with light and which one suits which space in our onyx colors guide.
How does Nyxora use onyx?
Nyxora is a sculptural lighting studio that makes handmade table lamps, wall sconces, and floor lamps from natural onyx in its Izmir atelier. Founded by interior architect Meyra Acar, the studio works only with natural onyx and marble; no synthetic marble or resin is used.
Each lamp takes shape in the atelier in the hands of a single artisan. The blocks are first examined under light, the form is placed according to the stone’s vein map, and the number of the block each lamp is cut from is recorded. Because each design is produced in limited numbers and the veining never repeats, no two lamps are identical. You can follow the journey from block to lamp step by step in our article on how an onyx lamp is made.
At the Nyxora studio, we see onyx less as a cladding material than as a record that light can read: each band tells of one period in the life of the water that formed the stone.
Frequently asked questions
Are onyx and marble the same stone?
No. Both contain calcite, but marble is a metamorphic rock formed when limestone is transformed by heat and pressure, while onyx is a sedimentary stone deposited layer by layer from spring or cave waters. Although onyx is sold as onyx marble in the stone trade, it is translucent, carries parallel bands, and is softer than marble. When it is backlit, the difference is immediately visible.
Is onyx a semi-precious stone?
Chalcedony onyx, which is used in jewelry, is traditionally counted among the semi-precious stones because it belongs to the quartz family. Calcite onyx, which is used in lighting and interior architecture, is a decorative natural stone. What makes it special is not its hardness but its translucency and a band pattern that differs in every block; that is why its character only fully emerges with light.
Is onyx a fragile stone?
Calcite onyx has a hardness of about 3 on the Mohs scale, which means it is softer than marble and more sensitive to impact. This does not mean it will cause problems in everyday use. An onyx lamp placed on a flat, stable surface and protected from falls and knocks can comfortably be part of daily life. For cleaning, only a dry, soft cloth should be used.
At what thickness does onyx let light through?
Depending on its type and band density, onyx can let light through even at a thickness of 1–2 cm; however, the thinner the stone, the stronger the glow and the lighter the colors. In Nyxora lamps, the body is carved down to a wall thickness of 6–12 mm depending on the model and the light source. White onyx has the most generous translucency, while the dark bands in river and blue onyx hold back more light.
How can you tell if onyx is real?
The strongest check you can do without harming the stone is the light test: when backlit, natural onyx glows layer by layer, its bands at different intensities. In addition, natural stone feels cool to the touch, is heavy for its size, and its bands continue uninterrupted across the edges. A scratch or acid test permanently damages the stone; for a definitive result, consult a stone specialist or a laboratory.