Explanation:

Odd One Out:
The odd one out in this list is Marble.

Reasoning:
To determine the odd one out, we need to analyze the characteristics of each item in the list and identify the one that does not fit the pattern or has different properties compared to the others.

Ruby:
- Ruby is a precious gemstone known for its red color.
- It is a type of corundum mineral and is valued for its beauty and rarity.
- Rubies are commonly used in jewelry.

Sapphire:
- Sapphire is also a precious gemstone that belongs to the corundum mineral family.
- It is known for its blue color, although it can occur in various other colors as well.
- Sapphires are widely used in jewelry and are highly valued.

Diamond:
- Diamond is a precious gemstone that is composed of carbon.
- It is known for its exceptional hardness and brilliance.
- Diamonds are highly valued and widely used in jewelry.

Marble:
- Marble is a type of metamorphic rock that is commonly used in construction and sculpture.
- It is not a gemstone and does not possess the same properties as rubies, sapphires, and diamonds.
- Marble is known for its smooth and polished appearance and is often used for decorative purposes.

Conclusion:
Based on the analysis of the properties and characteristics of each item, it is clear that Marble is the odd one out as it is not a gemstone like the other three options (Ruby, Sapphire, and Diamond). Marble is a type of rock, whereas the others are all precious gemstones valued for their beauty and rarity.