Onyx is a variety of chalcedony, which is a type of mineral made up of silicon dioxide (SiO2). The chemical properties of onyx stone are as follows:

1. Chemical formula: Onyx has the same chemical formula as other types of chalcedony, which is SiO2.

2. Composition: Onyx is composed of microcrystalline quartz, which is formed by the precipitation of silica from groundwater.

3. Mineralogy: Onyx is a type of cryptocrystalline quartz, which means that its crystals are too small to be seen with the naked eye.

4. Hardness: Onyx has a Mohs hardness of 6.5-7, which makes it relatively hard and durable.

5. Solubility: Onyx is insoluble in water and most acids, but it can be dissolved by hydrofluoric acid.

6. Reactivity: Onyx is generally inert and does not react with most chemicals or substances.

Overall, the chemical properties of onyx are similar to those of other types of chalcedony, and its composition and mineralogy are determined by its formation process.

The physical properties of onyx stone include:

1. Hardness: Onyx has a Mohs hardness of 6.5-7, which makes it relatively hard and durable.

2. Density: The density of onyx ranges from 2.55 to 2.70 g/cm³, which is similar to other types of chalcedony minerals.

3. Color: Onyx is typically found in shades of black, white, brown, red, and green. Its color is determined by the minerals present in the rock.

4. Luster: Onyx has a vitreous or glassy luster, which gives it a shiny appearance.

5. Transparency: Onyx can be translucent or opaque, depending on the thickness of the bands and the amount of impurities present in the rock.

6. Cleavage: Onyx does not have a distinct cleavage, but it can fracture along its bands.

7. Streak: Onyx has a white streak.

Overall, onyx is a unique and beautiful stone that has a distinctive banded appearance and a range of physical properties that make it suitable for a variety of decorative and functional applications.