They're too reactive. They will react with oxygen or moisture in the air, so they can't exist as pure elements unless protected. The usual method is to submerse them in oil.
uranium
Calcium is never found in its elemental form in nature.
Hafnium is an element not a rock. Hafnium is never found in nature pure form so does not fit into any groups. Hafnium is a chemical element, a metal placed in the group 4 and period 6 of the periodic table of Mendeleev.
group 1 elements
Group 1 and group 2 metals
The alkali metals
Because they are highly reactive with many other elements.
Calcium is commonly found in milk and milk products
Neodymium is never found in nature as a free element. It occurs in ores such as monazite and bastnasite. The main mining areas are China, United States, Brazil, India, Sri Lanka and Australia.
its an element, so yes, any thing that's not manufactured by man is natural, therefore found in nature. It is not, however, found unless forced by man; so for most practical purposes it is not found in nature.
Phosphorus, a nonmetallic chemical element, is a mineral and never found alone in nature. It is found in washing powder because it is useful for softening water and to prevent pipe corrosion.
Due to its high reactivity, phosphorus is never found as a free element on Earth. Inorganic phosphate rock, which is partially made of apatite is the chief commercial source of this element today.