The metallic grey gemstone cabochon shown here is 25mm long. It is available to be handcrafted into a custom made ring or pendant for you. Haematite is mined as the main ore of iron. Grey hematite is typically found in places where there has been standing water or mineral hot springs. There is haematite on Mars.
Haematite is thought to help reduce the discomfort of leg cramps and fractures; to cleanse the blood and assist with blood-related problems such as anaemia. It is believed to be inspirational while still keeping you grounded.
I used a similar cabochon to create this custom piece: