Question

What is the relative density of
seawater.
granite rock.
basaltic rock.
mantle

Answer 1

oh and @SraJMcGin, if you give me another link to the results of something you googled AGAIN, i may just loose my head. it doesn't help!

Answer 2

Seawater is just slightly over the fresh water density baseline of 1 dues to salt and trace minerals in it. Since all your other rocks sink in salt water, you know they are denser (Archimedes)
The mantle is composed of various materials and gets denser with depth, relative density goes from about 3.3 to 5.7
Good old Archimedes means the other rocks are less dense, since they float above the mantle. Here is a table:

Andesite 2.5 - 2.8
Basalt 2.8 - 3.0
Coal 1.1 - 1.4
Diabase 2.6 - 3.0
Diorite 2.8 - 3.0
Dolomite 2.8 - 2.9
Gabbro 2.7 - 3.3
Gneiss 2.6 - 2.9
Granite 2.6 - 2.7
Gypsum 2.3 - 2.8
Limestone 2.3 - 2.7
Marble 2.4 - 2.7
Mica schist 2.5 - 2.9
Peridotite 3.1 - 3.4
Quartzite 2.6 - 2.8
Rhyolite 2.4 - 2.6
Rock salt 2.5 - 2.6
Sandstone 2.2 - 2.8
Shale 2.4 - 2.8
Slate 2.7 - 2.8

Answer 3

mantle