Determining the Density of Matter

     What is density and how can it be calculated using the mass and volume of an object? Density (D = M / V) offers a convenient means of obtaining the mass of a body from its volume or vice versa; the mass is equal to the volume multiplied by the density (M = D x V), while the volume is equal to the mass divided by the density (V = M / D). The densities of rocks and minerals are normally expressed as specific gravity, which is the density of the rock relative to the density of water. As a general rule, non-metallic minerals have low densities while metallic minerals have high densities. Most of the major rock-forming minerals in the Earth's crust, like quartz, feldspar, and calcite, have very similar densities (around 2.6 to 3.0 g/cm3). Some of the heaviest metallic minerals, like iridium and platinum, can have densities as high as 20. Rock density is very sensitive to the minerals that compose a particular rock type. Sedimentary rocks (and granite), which are rich in quartz and feldspar, tend to be less dense than volcanic rocks.  By using a cream-rich snack cake to practice density calculations, the densities rock/stones/minerals can be found in a similar manner.

Procedure

Materials: 2-3 / group

Twinkie

Rock/Stone/Mineral (about equal size of a Twinkie)

Electronic Scale (set to grams)

Spoon

500 mL Graduated Cylinder

Calculator

Resources

Steps:

1.      Gather all necessary materials as directed and unwrap the Twinkie.

2.      Determine the Mass of the Twinkie by measuring and recording the Mass (in grams) on the data result sheet (#1).

3.      Determine the Volume of the Twinkie (via a water displacement method) by adding 350 mL of water into a 500 mL graduated cylinder.

4.      Slowly and carefully, completely submerge the Twinkie into the water; use the end of a spoon to help.

5.      Record, on your data result sheet (#2), how high the water went in the 500 mL graduated cylinder; then, remove the water and Twinkie over a sink and dispose the Twinkie appropriately.

6.      Subtract the water reading “after” the Twinkie was submerged from the reading “before” the Twinkie was submerged and record the answer on the data result sheet (#3).

7.      Determine the Density of the Twinkie by using the following formula: D = M (grams) / Volume (milliliters) and record the value on the data result sheet (#4).

8.      Repeat steps 2-6 in a “similar” way; however, determine the Mass, Volume, and eventually the Density of a rock/stone/mineral provided. Record the answers on the data result sheet (#’s 5-8).   

9.      Answer all further questions on the data result sheet.

10.  Return all materials as directed and clean your area.

 

                     

 

 

 

Examples of Mineral and Rock Densities

 

Mineral

Density

Rock

Density

Apatite

3.1–3.2

Andesite

2.5–2.8

Biotite Mica

2.8–3.4

Basalt

2.8–3.0

Calcite

2.71

Coal

1.1–1.4

Chlorite

2.6–3.3

Diabase

2.6–3.0

Copper

8.9

Diorite

2.8–3.0

Feldspar

2.55–2.76

Dolomite

2.8–2.9

Fluorite

3.18

Gabbro

2.7–3.3

Garnet

3.5–4.3

Gneiss

2.6–2.9

Gold

19.32

Granite

2.6–2.7

Graphite

2.23

Gypsum

2.3–2.8

Gypsum

2.3–2.4

Limestone

2.3–2.7

Halite

2.16

Marble

2.4–2.7

Hematite

5.26

Mica schist

2.5–2.9

Hornblende

2.9–3.4

Peridotite

3.1–3.4

Iridium

22.42

Quartzite

2.6–2.8

Kaolinite

2.6

Rhyolite

2.4–2.6

Magnetite

5.18

Rock salt

2.5–2.6

Olivine

3.27–4.27

Sandstone

2.2–2.8

Pyrite

5.02

Shale

2.4–2.8

Quartz

2.65

Slate

2.7–2.8

Sphalerite

3.9–4.1

 

 

Talc

 

2.7–2.8

 

 

Tourmaline

 

3.02–3.2