Padmala

Malas are traditionally made by hand and each bead is separated by a Brahma Granthi, or the knot of Brahma, the creator. This knot is specific to malas and each knot, as the mala is made, is tied with the mantra Om thus emphasising the intention of meditation.

Offset from the main loop of beads is the sumeru, or mountain bead and tassel to mark the end or return point when using the mala for mantra. This is sometimes referred to as the guru bead, and, just like the guru, should not be crossed.

The traditional use of a mala for the purpose of counting mantras correlates with many other religious/spiritual practices where beads are used for the repetition of prayers, i.e. rosaries or prayer beads.

The different materials the malas are made from have a direct influence on our physical bodies (for example rudraksha, has been found to lower blood pressure) and also have an influence on our pranic, or energetic, bodies and this is why many people choose to wear them.

Sumerini

The 27 bead mala, known as sumerini, conveniently slips onto the wrist and wearing one like this can have the same effects as wearing one around the neck, with the added advantage of always being visible. Sumerini malas may also have 18 beads. 27 and 18 are divisions of 108

Why 108?

There are many ideas about the significance of 108, but one of the most common is that 1 represents the supreme consciousness, 8 represents the eight aspects of nature consisting of the five fundamental elements of earth, water, fire, air and ether, plus ahamkara (individuality), manas (mind) and buddhi (sense of intuitional perception) and 0 represents the cosmos, the entire field of creation. To put it another way: 1 is Shiva, 8 is Shakti and 0 is their union or yoga.

Actually, it's not 108, it's one, zero, and eight. One represents the Purusha (the male, solar energy, the seed, the potential), eight – Prakriti (feminine, mental energy, engine, nature, manifestation), a zero is nothingness, shunya or emptiness.
When Purusha and Prakriti come together, there is creation – 1+8=9, and if you take all the multiples of 9 – 9x2=18, 9x3=27, 9x4=36, 9x5=45, each sum when added together becomes 9! All multiples of 9 are 9 and that never changes.
Whatever duality or destruction there is, the creation is there, the universe is there, the creation continues. But remember that creation has no beginning and no end.
It was, it is and it will be! And it is exactly 108. One is Purusha and eight is Prakriti, but if we separate Prakriti from Purusha, we get vacuum, shunya, non-presence, emptiness, silence. This is Yoga. The number 108 represents the process of Yoga, the separation of Purusha from Prakriti by creating a void, which is called samadhi or dhyana.
Nothingness is zero when the mind becomes still and calm, there are no waves. The state of shunya arises when the mind is completely empty of any experience: conscious, subconscious or unconscious. Shunya or emptiness, nothingness, separates Purusha from Prakriti, samadhi separates Purusha from Prakriti, and that is the meaning of 1-0-8.
Swami Satyananda Saraswati

The Chakras are pranic or energy centres within the human body.
According to the Tantric tradition these chakras govern a particular region of the body, specific glands, sense organs, etc. and are responsible for the expression of our personality and our ability, or lack of, to express ourselves fully in the world.
Each chakra has a particular colour and stone associated with it, wearing malas made of stones associated with a specific chakra can help activate and balance the qualities associated with that particular chakra.

Sahasrara
Transparent and white minerals and crystals.
Amethyst, Analcime, Apophyllite, Aqua Aura, Beryl, Citrine, Clear Tourmaline-Achroite, Fluorite, Howlite, Labradorite, Mica, Opal, Rock Crystal, White Apatite, White Coral, White Iceland Spar, White Magnesite, White Pearl, Zircon.

Ajna
Indigo-blue and purple minerals and crystals balance, clear and stimulate thinking.
Amethyst, Blue & Violet Spinel, Blue Opal, Blue Sapphire, Blue Tourmaline, Lolite (Cordierite), Moonstone, Petersite, Sodalite, Sugilite, Tanzanite, Violet Fluorite, Violet Jadeite, Violet Kunzite, Violet Lazurite (Lapis Lazuli).

Vishuddhi
Blue and gray minerals and crystals balance, clear and contribute to deep calmness.
Amazonite, Aquamarine, Aquamarine, Azurite, Blue Amazonite, Blue Apatite, Blue Chalcedony, Blue Druzy, Blue Fluorite, Blue Kyanite (Disten), Blue Obsidian, Blue Quartz Crystal, Blue Spinel, Blue Topaz, Blue Tourmaline–Indigolite, Celestine, Chrysocolla, Gray & Blue Agate, Gray Onyx, Hawk Eye, Labradorite, Lapis Lazuli, Moonstone, Mother of Pearl, Opal, Prenite, Sapphire, Sapphire, Sodalite, Tanzanite, Turquoise.

Anahata
Green and Pink minerals and crystals balance and clear it. They stimulate heart activity, relieve tension. They affect all organs in the heart area and restores cells.
Amazonite, Aventurine, Chrysoberyl (Beryl), Chrysocolla, Nephrite, Chrysoprase, Dioptase, Emerald, Garnet–Uvarovite (Green), Green Apatite, Green Apophyllite, Green Kyanite (Disten), Green Opal, Green Quartz, Green Sapphire, Green Serpentine, Green Tourmaline–Verdelite, Heliotrope, Jadeite, Larimar, Malachite, Moldavite (Voltavine), Moonstone, Morganite (Pink Beryl), Mossy Agate, Olivine (Chrysolite, Peridot), Pink Calcite, Pink Coral, Pink Fluorite, Pink Iceland Spar, Pink Kunzite, Prasem, Prenite, Rhodochrosite, Rhodonite, Rose Quartz, Ruby, Smaragd (Emerald), Unakite, Watermelon Tourmaline.

Manipura
Yellow minerals and crystals balance and clear it. They affect the nervous and digestive systems. They stimulate digestion and the release of gastric juice.
Amber, Chrysoberyl, Citrine, Diamond, Fire Agate, Fire Opal, Golden Beryl, Golden Gemstone, Heliodor, Lemon Quartz, Pyrite, Rutile Quartz, Sunstone, Yellow Chalcedony, Yellow Fluorite, Yellow Jasper, Yellow Quartz Crystal, Yellow Tiger Eye, Yellow Topaz, Yellow Tourmaline, Zircon.

Swadhisthana
Orange minerals and crystals balance and heal her, activate endocrine glands, improve metabolism and provide creative energy.
Amber, Carnelian (Carnelian), Citrine, Fossilized Coral, Garnet, Garnet-Almandine, Heliodor, Orange Chalcedony, Orange Chrysolite, Orange Fire Agate, Orange Jasper, Orange Quartz Crystal, Precious Pearls, Red Jasper, Ruby, Tiger's Eye, Topaz.

Mooladhara
Red minerals and crystals heal and balance it. They eliminate fatigue and have a toning effect on the body. Black and brown minerals and crystals heal and balance it, strengthen resistance forces, calm the entire energy flow and reduce pain.
Agate (in red tones), Andalusite (in red tones), Biotite, Black Jadeite, Black Quartz Crystal, Black Tourmaline, Brown DruzyBrown Tiger's Eye, Garnet, Haematite, Heliotrope, Morion, Obsidian, Onyx, Opal (black, red),Red Carnelian, Red Coral, Red JasperRed Tiger's Eye, Reddish Chalcedony, Ruby, Smoky Quartz, Staurolite.