These shapes also may occur naturaly in stones and the meanings and  practical applications for these shapes are basicly the same for both carved and natural stones.  Many people feel that naturaly shaped stones have more "medicine" than carved shaped stones.

Spheres

Crystal spheres or balls are  often used in scrying, They are used in healing and  in room and area  clearing and protection  and for virtually any purpose. They radiate the properties of  the material from which they are made or the programs they are  given  evenly in all directions. A sphere represents completion, and  the realization of all possible things . It has no
beginning or end.  Spheres represent the achievement of wholeness and revealing of the inner beauty  and perfection of our spirit. Spheres help us stay centered in the present.  They make excellent altar pieces and can be the focus of many meditations.

Eggs

Egg shaped stones are easy to hold and can be used in massage  they are said  to assist with stress reduction
I am leaving some of the more unusual uses for eggs to the adult imagination but the egg symbolizes fertility, a fertilized egg eventually becomes a living being. The egg shape symbolizes the potential and developmental  stage  of our goals and dreams.
The egg also symbolizes the void, the unknown and unformed from which form and  realization are born.
 Meditate, holding an egg shaped stone of an appropriate  material in your hand (or have it set
before  you at eye level ) on any condition or situation which you would like to transform or bring  into reality.
You can meditate on an egg to help you develop clarity about what you wish to manifest in your life particularly in spiritual evolution.You can also ask/program your egg to assist in manifesting  the results you have visualized.

Some people meditate while they sit on an egg shaped stone or crystal so that it puts pressure between the genitals  and excretory organ  this is said to connect the  upward and downward flow of your natural chi and assist in spiritualizing your being.
Eggs can also be used  in grids or for programs to support fertility childbearing  and nurturing  of all kinds.

 Another meditation visualization involving eggs  is to imagine  yourself  inside an egg  of light. This is a powerful protective visualization. You can imagine yourself inside an egg and to imagine yourself hatching.  This can help you  in identifying both areas where you are blocking  your self and  help you release those blockages and restraints and reach more personal/ spiritual freedom.  Egg shaped stones are often used in massage and energy healing work because of the soft dispersion of energies.
 

Pyramids

One of the functions of a pyramid is to draw spiritual energy through the point and to ground it at the base.  It helps to blend spiritual and physical energies.  Thus, it can be very effective in dissolving mental and emotional blockages. It can help with grounding and can help reveal personal subconscious mysteries to the conscious self.
It can be used for integrating and harmonizing  aspects of your personality subconscious and spirit. they create large energy fields around themselves and are therefore useful for energizing large rooms and spaces.

Obelisks

Are said to generate an energy field similar to the human aura  They can create a powerful
focus and have  a  balancing effect on the chakras and subtle bodies .
 

Skulls

Crystal skulls are record keepers. They amplify energy. They develop holograms in them from their experiences.  There are old crystal skulls that exist in the  physical. Many skulls are made from very old crystal possibly 10,000 years old, and are
very powerful.  Some seem to be encoded with messages.  They have picked up many frequencies through their time here. Some ancient skulls  are well known for energizing people and allowing them to access visions and information .
Contemporary crystal skulls are sometimes  used for  scrying and  meditation.

Hearts

One of the most common carved forms for rocks and gemstones is the heart shape. This shape is a  symbol of love and is often exchanged as a gift of love and affection. The stone hearts are available in many stones and can be used for many kinfds of crystal healing. They  are often part of   love, romance and healing grids . Hearts are widely available and  can be used in general healing layouts and for chakra work too. 

Donuts 

Also very common carved shape. In metaphysics, it's a halo—sign of divine dimension and intention.
I have begun an attempt to understand the metaphysics of this form but so far it is very compicated about inverse tetrhedrons and the shape of the universe and manifesting  the divine from the void . I'll need to study more.

Carved images

Many crystals and stones are carved into animal and  images such as angels and Gods/esses which can be used for meditation and to help you connect with a totem or power animal .

there are also traditional associations for many naturaly shaped stone forms.