Heidi and Spencer Pratt Show Off Human-Size Crystals and Massive Self-Portraits on MTV's 'Cribs'

Heidi and Spencer Pratt are welcoming fans into their one-of-a-kind crib!

In a sneak peek of the next episode of MTV Cribs (airing Dec. 1), Heidi, 36, shares that she and and Spencer, 39, have a pretty obvious theme in their decor: "lots of crystals."

They show off an enormous white crystal the size of a child that seems to be emanating colored light. Heidi — who is holding her baby bump as the episode was filmed before she and Spencer welcomed their second child, son Ryker, earlier this month — reveals "is the first crystal we ever bought, or Spencer was ever drawn to."

Spencer jokes of the formation, "We were told that it was from a volcano in Peru. We were definitely lied to. It's for sure from Brazil, out of a mine. But you know, it was a good salesmen out there."

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MTV

They move on to a large citrine and a "quartz cluster," before introducing a special carved item.

"This is a lepidolite elephant for healing. It has lithium so that's where they get that," Heidi says of one of the pieces on display.

Spencer describes it as "a big Xanax of crystals."

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MTV

The Hills alums head to their dining area, which features large-scale portraits of the pair spanning one wall.

Heidi notes that the photos were captured by famed photographer Martin Schoeller, who is known for his highly detailed close-ups of faces. "Martin Schoeller is an incredible photographer. And it was a great investment into ourselves," Heidi says.

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The episode comes months after Heidi showed off their "life changing" home organization makeover before becoming a family of four.

"I've been waiting to do the nursery for a while, looking for just the right time because I wanted to change Gunner's room into the nursery," The Hills: New Beginnings star told PEOPLE of her and Spencer's now 5-year-old son in August. "I've been waiting to transition him to a different room in the house."

Before she could make that happen, Heidi had a junk closet to tackle. "I have had a collection of what my husband would call treasure for the past five years that's built up in that room," Heidi admitted.

MTV

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"I spent eight hours in there trying to throw things away and organize, and it just felt really overwhelming," she said.

Enter professional organizer Eryn Donaldson, CEO of The Model Home, who helped Heidi tackle the clutter and reach her organizational goals.

"What Eryn did was incredible," Heidi says. "I was going to fly my mom out to help with this and then I thought, 'well this is even better.'"

MTV's Cribs airs Thursdays (9 p.m. ET) on MTV.