A birthstone is a gift of a precious material (jewelry, mainly gemstones; themselves traditionally associated with various qualities) that symbolizes the month of birth in the Gregorian calendar. It is sometimes also called birthday stone (cf. infra; but that word is, confusingly, sometimes used as a synonym for an anniversary gift, which is related to the recipient's age, that is, year of birth).

By her who in this month (January) was born
No gem save garnets should be worn;
They will ensure her constancy,
True friendship, and fidelity.

The February-born shall find
Sincerity and peace of mind,
Freedom from passion and from care,
If they an amethyst will wear.

Who in this world of ours their eyes
In March first open shall be wise,
In days of peril firm and brave,
And wear a bloodstone to their grave.
(In modern times, the bloodstone has been replaced by the aquamarine.)

She who from April dates her years,
Diamond shall wear, lest bitter tears
For vain repentance flow, this stone,
Emblem of innocence, is known.

Who first beholds the light of day
In spring's sweet flowery month of May
And wears an emerald all her life
Shall be a loved and happy wife.

Who comes with summer to this earth,
And owes to June her hour of birth,
With ring of agate on her hand
Can health, wealth, and long life command.
(In modern times, the agate has been replaced by the pearl.)

The glowing ruby shall adorn,
Those who in July are born;
Then they'll be exempt and free
From love's doubts and anxiety.

Wear a sardonyx or for thee,
No conjugal felicity;
The August-born without this stone,
`Tis said, must live unloved and lone.
(In modern times, the sardonyx has been replaced by the peridot.)

A maiden born when September leaves
Are rustling in September's breeze,
A sapphire on her brow should bind
`Twill cures diseases of the mind.

October's child is born for woe,
And life's vicissitudes must know,
But lay an opal on her breast,
And hope will lull those woes to rest.

Who first comes to this world below
In dreary November's fog and snow,
Should prize the topaz's amber hue,
Emblem of friends and lovers true.

If cold December gave you birth,
The month of snow and ice and mirth,
Place on your hand a turquoise blue;
Success will bless whate'er you do.

-- Gregorian birthstone poems