We often get asked - what is the birth stone for *insert star sign* or *insert birth month*?
Well If you want to select crystals that way, here are the following suggestions below (note that there are slight variations depending on the sources you read and some suggestions also seem contradictory depending if you're going by the month or the sign).
While there's nothing wrong with selecting crystals this way, please don't get too invested in it.  We will always believe that the best method in selecting crystals is being guided by your intuition.  In other words, the crystals you feel drawn to the most (for whatever reason) or the one that caught your eye first, are probably the ones you need most for where you are currently at right now.

BY MONTH:

JANUARY
Main Crystal - Garnet

FEBRUARY
Main Crystal - Amethyst
Alternative Crystal - Pearl

MARCH
Main Crystal - Aquamarine
Alternative Crystal - Bloodstone

APRIL
Main Crystal - Diamond
Alternative Crystal - Topaz

MAY
Main Crystal - Emerald

JUNE
Main Crystal - Pearl
Alternative Crystal - Moonstone

JULY
Main Crystal - Ruby

AUGUST
Main Crystal - Peridot
Alternative Crystal - Sardonyx

SEPTEMBER
Main Crystal - Sapphire

OCTOBER
Main Crystal - Pink Tourmaline
Alternative Crystal - Opal

NOVEMBER
Main Crystal - Citrine
Alternative Crystal - Blue Topaz

DECEMBER
Main Crystal - Turquoise
Alternative Crystal - Lapis Lazuli

BY STAR SIGN:

AQUARIUS (21/1 - 19/2)
Garnet

PISCES (20/2 - 20/3)
Amethyst

ARIES (21/3 - 20/4)
Bloodstone

TAURUS (21/4 - 21/5)
Sapphire

GEMINI (22/5 - 21/6)
Agate

CANCER (22/6 - 22/7)
Emerald

LEO (23/7 - 22/8)
Onyx

VIRGO (23/8 - 23/9)
Carnelian

LIBRA (24/9 - 23/10)
Peridot

SCORPIO (24/10 - 22/11)
Beryl

SAGITTARIUS (23/11 - 21/12)
Blue Topaz

CAPRICORN (22/12 - 20/1)
Ruby