Minor Characters/Gems

Minor Gem Characters are Gems who have debuted and been identified, but, as of yet, hold no significant nor recurring roles.

"Legs From Here to Homeworld"
Many Aquamarines appeared in cameos of "Legs From Here to Homeworld" cheering alongside with other Gems as Pink Diamond's Ship landed on Homeworld.

"Together Alone"
Four Aquamarines are visible at the Era 3 ball in "Together Alone" (two lifting the curtain for Yellow Diamond, then two more lifting the curtain for Blue Diamond):

Jades
Several Gems that are presumably Jades can be seen attending the Era 3 Ball in "Together Alone". They appear as two different types, with each type having two shades.

Two Gems of these types fuse after they see Stevonnie, Garnet, and Opal form, and they are subsequently poofed by Yellow Diamond.

Quartz
All Amethysts shown thus far, including the Crystal Gems' Amethyst, are voiced by Michaela Dietz.

All Jaspers (including "Skinny" and Pink Diamond's Jasper) and the defective Carnelian are voiced by Kimberly Brooks.

All Amethysts, Jaspers, and Carnelians stationed at Pink Diamond's Zoo were made on Earth, and were subordinates of Pink Diamond, until being reassigned to Blue Diamond after she was shattered.

History
Four Amethysts appear in "Gem Heist"; two of them are in charge of guarding the door in the Zoo's cargo bay. The two Amethysts tease the Crystal Gems when they land on the Zoo, resulting in a scolding from Holly Blue Agate. Later in "Gem Heist," another pair of Amethysts send Steven into the Zoo's tunnel, one with a square-faceted gemstone.

In "The Zoo," several Amethysts are seen entering the boundaries of Pink Diamond's Zoo to console the heartbroken Zoomans. One Amethyst later angrily informs Greg and Steven of the trouble they are in.

In "That Will Be All", this turns out to be a prank by Amethyst and the many other Homeworld Quartz guards she has met (whom she refers to collectively as "the Famethyst"), three of which having been formed right above her. These Amethysts inform her of her serial number being Facet-5 Cut-8XM. Among the Amethysts and Jaspers are two defective Gems: "Skinny", a tall and skinny Jasper, and Carnelian, shorter than most Quartz.

From this interaction, it can be assumed that Quartz Gems are generally good-natured (with Jasper and Holly Blue Agate being exceptions), as "the Famethyst" does not hold any grudge against the Crystal Gems.

In "Now We're Only Falling Apart", numerous Amethysts are shown emerging out of the Prime Kindergarten in a flashback from Pearl.

In "Together Alone", several Amethysts and Jaspers are shown in the crowd of Quartz Gems dancing alongside the Crystal Gems' Amethyst during the Era 3 Ball.

"Now We're Only Falling Apart"
Many Amethysts appear in Pearl's flashback, all of which emerging from the Prime Kindergarten.

"Together Alone"
Several Amethysts attend the Era 3 ball, seen dancing along with several Jaspers.

"That Will Be All"
Several Jaspers from the Beta Kindergarten debuted in That Will Be All. Like the Amethysts, they originally belonged to Pink Diamond but now served Blue. Despite their gem type, they are all considered members of The Famethyst.

"Together Alone"
Two identical Jaspers attend the Era 3 ball, seen dancing along with several Amethysts.

Rubies
All Rubies shown thus far, including the Crystal Gems' Ruby, are voiced by Charlyne Yi.

"The Answer"
Two Rubies appear in Garnet's flashback in "The Answer". They were sent (along with the Crystal Gem Ruby) to Earth to escort Sapphire to Blue Diamond. They was poofed by Pearl, and their fates are unknown.

They appear to be identical to the Crystal Gem Ruby and each other in appearance, clothing, and voice. Both Rubies seem to be obsessed with fighting.

They have identical gemstones in different locations.

"Together Alone"
Several Rubies are seen attending the "Era 3 Ball" in "Together Alone", accompanying various Sapphires.

The Rubies salute "Pink Diamond" (Steven), and many appear Sapphires appear later at the dance.

Sapphires
Various Sapphires are seen attending the Era 3 Ball in "Together Alone".

The Sapphires salute "Pink Diamond" (Steven), accompanied by various Rubies when approaching Steven.

Many Sapphires appear later at the dance.

Topazes
Two Topazes appear, non-speaking, in a flashback in "Now We're Only Falling Apart" alongside Pearl, Rose Quartz, and three Amethysts. One Topaz has her gemstone on her navel, while the other's gemstone placement is unknown. Four more are seen in the episode, "Familiar". The first two are seen guarding Yellow Diamond's extraction chamber, the other two are seen guarding Blue Diamond's pool chamber, each holding a mace.

Ruby (triple fusion)
Ruby (triple fusion) is the fusion of all three Rubies in "The Answer", one of which is the Crystal Gem, Ruby.

As their individual forms and gemstones are the same, their fusion remains identical except much larger in size. In this form, they are much more powerful. However, the actual extent of their strength in this form remains unclear because they fought against Rose Quartz, who is actually Pink Diamond in disguise. The Crystal Gem Ruby describes the fusion as just "me, but bigger," implying the state of being is not that different for her unfused.

Trivia

 * So far, it is true that Gems of the same gemstone also share the same voice (with the exceptions of the Diamonds and White Pearl), albeit with some differences in tone. Their appearances are also nearly identical, excluding gemstone placement and minor outfit details.
 * Both Carnelian and "Skinny" Jasper were voiced by Kimberly Brooks, despite being two different types of quartz.
 * In "Hit the Diamond", it is revealed that Rubies are typically unintelligent and easily fooled. As Rubies are the Gem equivalent to foot soldiers and common enough to be effectively expendable, high intelligence isn't a necessity.
 * According to Ian Jones-Quartey, if the Pearls fused, they would form a bigger Pearl with combined colors.
 * This idea is shown when the Rubies and Topazes fuse.