Is there any mineral, chemical, or substance that is invisible?

Question

I am talking about an item that I can hold in my hand that I won't see or something similar to that.

Answer 1

all matter is visible to some extent
but there are gases that are almost transparent

? do you notice the gases that fill your hand ?

if you put your hand in water you can hold glass or diamonds and not see them

Answer 2

If you're reffering to solid substance, than you should be able to see it. It won't be completely invisible. Wether you can see it or not depends on your eyes' sensitivity. Why is that? Because a solid substance, when it's not light permeable, will blok the rays of light or reflects the rays of light, causing us to see it.
When it's light permeable, such as glass, it'll refract the rays of light due to the difference of density between the substance and the air. Rays of light travel slower in more dense substances. So when you see a very clear window, as long as you can see the edge, you would know it's there, because the rays passes through the substance are refracted even in very little amount, compared to the rays that passes through thin air.
But when you're surrounded by that substance, say you're in a completely sealed glass sphere, than you wouldn't see it, simply because your eyes cannot differentiate the light that passes through the glass and the light that passes through the thin air. Your eyes are playing trick on you in this case.

Answer 3

Glass, for one. Ever walk into a recently cleaned glass door?

Answer 4

Many. Oxygen being one. Think of all the gases.

Answer 5

Only gasses. You can't really hold then in your hand though.

Answer 6

dark matter.

it was just recently proven to exist. you can't see it in any wavelength of light.