No conversion is necessary. If something is 6 linear feet tall, it is 6 feet tall. It should be noted, that the correct term is Linear, since Lineal refers to a line of ancestry, not to length. There are times when the term Linear is used, and times when it is not. I'll give some examples of them. First a definition. Linear means a straight line so a straight line from point A to point B is the linear distance. One example would be... It is 2200 linear miles from Seattle to Washington DC. But if you were to drive from Seattle to Washington DC, you would have to drive 2700 miles.
Intrusive igneous rock contains large mineral crystals. The large crystals in intrusive igneous rocks form when magma cools very slowly. Magma that is trapped beneath Earth's surface is insulated by surrounding rocks, and cools and hardens over very long periods. Intrusive igneous rock contains large mineral crystals.
The inside of the Earth is very hot - hot enough to melt rocks. Molten (liquid) rock forms when rocks melt. The molten rock is called magma. When the magma cools and solidifies, a type of rock called igneous rock forms. What are they like? Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals. You may have done an experiment at school with a substance called salol. If molten salol cools slowly, you get big crystals.